staging: iio: dummy: replace block comment with single line comment

Replace one block comment with a single line comment. Follow style of
previous comment and omit word channel, since it's clear the topic is
channels.

Addresses checkpatch.pl:
WARNING: Block comments use * on subsequent lines
Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/iio_simple_dummy.c

@@ -364,8 +364,7 @@ static int iio_dummy_read_raw(struct iio_dev *indio_dev,
 				ret = IIO_VAL_INT_PLUS_MICRO;
 				break;
 			case 1:
-				/* all differential adc channels ->
-				 * 0.000001344 */
+				/* all differential adc -> 0.000001344 */
 				*val = 0;
 				*val2 = 1344;
 				ret = IIO_VAL_INT_PLUS_NANO;