staging:iio:adxrs450: Use usleep_range for the sequential transfer dealy

The adxrs450 requires a delay of at least 0.1 ms between register writes.  Using
msleep() for such small delays is not recommended. So use usleep_range instead.

Fixes the following checkpatch warning:
	WARNING: msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.txt
	+	msleep(1);

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/gyro/adxrs450_core.c

@@ -101,7 +101,7 @@ static int adxrs450_spi_write_reg_16(struct iio_dev *indio_dev,
 	if (ret)
 		dev_err(&st->us->dev, "problem while writing 16 bit register 0x%02x\n",
 			reg_address);
-	msleep(1); /* enforce sequential transfer delay 0.1ms */
+	usleep_range(100, 1000); /* enforce sequential transfer delay 0.1ms */
 	mutex_unlock(&st->buf_lock);
 	return ret;
 }