iio:gyro:itg3200 - drop unreachable return ret. Highlighted by smatch

CHECK   drivers/iio/gyro/itg3200_core.c
drivers/iio/gyro/itg3200_core.c:114 itg3200_read_raw() info: ignoring unreachable code.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: Neil Brown <neilb@suse.de>
Cc: Dan Carpenter <dan.carpenter@oracle.com>