Staging: iio: adc: Refine delay computation

As per comment in function ad7280_delay, conversion delay may take up
to 250us. We cannot rely on msleep for this because it may sleep longer
than intended time for values less than 20ms, so use usleep_range instead.

Problem detected using checkpatch.pl.
Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/adc/ad7280a.c

@@ -188,7 +188,7 @@ static void ad7280_delay(struct ad7280_state *st)
 	if (st->readback_delay_us < 50)
 		udelay(st->readback_delay_us);
 	else
-		msleep(1);
+		usleep_range(250, 500);
 }
 
 static int __ad7280_read32(struct ad7280_state *st, unsigned *val)