Staging: iio/accel: Changed data type of val in store_measurement_mode to u8

The code in sca3000_store_measurement_mode() uses the variable val to
do bitwise operations with an int mask and or-s it into st->rx[0] which
is an entry in a u8 array (see sca3000.h).

This means up to now values larger than a u8 were silently ignored and
just the lower 8 bits counted into the value that was written into
st->rx[0]. This code will return -ERANGE if the value in buf was too
large to fit into a u8.

Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>