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>