iio: imu: st_lsm6dsx: make st_lsm6dsx_check_odr() non-static

Remove static qualifier from st_lsm6dsx_check_odr() definition in order to
use it for the support of new devices

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>