iio: imu: st_lsm6dsx: unlock on error in st_lsm6dsx_shub_write_raw()

We need to release a lock if st_lsm6dsx_check_odr() fails, we can't
return directly.

Fixes: 76551a3c ("iio: imu: st_lsm6dsx: specify slave odr in slv_odr")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>