Staging: iio/accel: Added a range check for val in store_measurement_mode()

In sca3000_store_measurement_mode() we use val to and it with a mask.
This mask is only two bits long (as we are only interested in the
lowest two bits), so a value bigger than 3 was silently ignored so
far.

Now this function will return -EINVAL, if val is bigger than 3.

Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>