Explicitly ignore error at many call sites for clarity

Used the following:
  go get github.com/kisielk/errcheck
  errcheck -ignore 'Close|rintf' ./...

While some are irrelevant, there were some genuine issues so this is worth
enforcing, hence a few innocuous places were 'fixed' so that the list could go
down to zero.

Do not enforce this in travis yet, but should be done soon.

devices/apa102/apa102_test.go

@@ -1079,7 +1079,9 @@ func BenchmarkHalt(b *testing.B) {
 	d, _ := New(spitest.NewRecordRaw(ioutil.Discard), &DefaultOpts)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		d.Halt()
+		if err := d.Halt(); err != nil {
+			b.Fatal(err)
+		}
 	}
 }
 

experimental/devices/mpu9250/mpu9250.go

@@ -91,8 +91,9 @@ func (m *MPU9250) Init() error {
 // Calibrate Calibrates the device using maximum precision for both Gyroscope and Accelerometer.
 func (m *MPU9250) Calibrate() error {
 
-	m.transferBatch(calibrateSequence, "error calibrating %d: [%x:%x] => %v")
+	if err := m.transferBatch(calibrateSequence, "error calibrating %d: [%x:%x] => %v"); err != nil {
-
+		return err
+	}
 	reads, err := m.GetFIFOCount() // read FIFO sample count
 	if err != nil {
 		return wrapf("can't get FIFO => %v", err)

experimental/devices/unicornhd/unicornhd.go

@@ -59,8 +59,7 @@ func (device *Dev) String() string {
 // Halting the unicorn HD sets all the pixels to black. Error is always nil.
 func (device *Dev) Halt() error {
 	black := color.RGBA{0, 0, 0, 0}
-	device.Draw(device.Bounds(), &image.Uniform{black}, image.ZP)
+	return device.Draw(device.Bounds(), &image.Uniform{black}, image.ZP)
-	return nil
 }
 
 // ColorModel implements devices.Display. There's no surprise, it is

experimental/devices/unicornhd/unicornhd_test.go

@@ -82,8 +82,9 @@ func TestHalt(t *testing.T) {
 	}
 	buf := bytes.Buffer{}
 	dev, _ := NewUnicornhd(spitest.NewRecordRaw(&buf))
-
+	if err := dev.Halt(); err != nil {
-	dev.Halt()
+		t.Fatal(err)
+	}
 
 	if !bytes.Equal(expectedAllBlack, buf.Bytes()) {
 		t.Fatalf("%#v != %#v", expectedAllBlack, buf.Bytes())
@@ -163,8 +164,9 @@ func TestDrawWritesBlackImageToSpi(t *testing.T) {
 	buf := bytes.Buffer{}
 	dev, _ := NewUnicornhd(spitest.NewRecordRaw(&buf))
 	black := color.RGBA{0, 0, 0, 0}
-
+	if err := dev.Draw(dev.Bounds(), &image.Uniform{black}, image.ZP); err != nil {
-	dev.Draw(dev.Bounds(), &image.Uniform{black}, image.ZP)
+		t.Fatal(err)
+	}
 
 	if !bytes.Equal(expectedAllBlack, buf.Bytes()) {
 		t.Fatalf("%#v != %#v", expectedAllBlack, buf.Bytes())
@@ -217,8 +219,9 @@ func TestDrawWritesWhiteImageToSpi(t *testing.T) {
 	buf := bytes.Buffer{}
 	dev, _ := NewUnicornhd(spitest.NewRecordRaw(&buf))
 	white := color.RGBA{255, 255, 255, 255}
-
+	if err := dev.Draw(dev.Bounds(), &image.Uniform{white}, image.ZP); err != nil {
-	dev.Draw(dev.Bounds(), &image.Uniform{white}, image.ZP)
+		t.Fatal(err)
+	}
 
 	if !bytes.Equal(expectedAllWhite, buf.Bytes()) {
 		t.Fatalf("%#v != %#v", expectedAllWhite, buf.Bytes())
@@ -288,7 +291,9 @@ func TestDrawWritesSequenceImageToSpi(t *testing.T) {
 			img.Set(x, y, clr)
 		}
 	}
-	dev.Draw(dev.Bounds(), img, image.ZP)
+	if err := dev.Draw(dev.Bounds(), img, image.ZP); err != nil {
+		t.Fatal(err)
+	}
 
 	if !bytes.Equal(expectedSequence, buf.Bytes()) {
 		t.Fatalf("%#v != %#v", expectedSequence, buf.Bytes())
@@ -349,8 +354,9 @@ func TestDrawSupportsPartialUpdates(t *testing.T) {
 	buf := bytes.Buffer{}
 	dev, _ := NewUnicornhd(spitest.NewRecordRaw(&buf))
 	white := color.RGBA{0xFF, 0xFF, 0xFF, 0xFF}
-
+	if err := dev.Draw(image.Rect(0, 0, 3, 3), &image.Uniform{white}, image.ZP); err != nil {
-	dev.Draw(image.Rect(0, 0, 3, 3), &image.Uniform{white}, image.ZP)
+		t.Fatal(err)
+	}
 
 	if !bytes.Equal(expectedWhiteSquare, buf.Bytes()) {
 		t.Fatalf("%#v != %#v", expectedWhiteSquare, buf.Bytes())