iio: imu: st_lsm6dsx: simplify data ready pin parsing

Simplify st_lsm6dsx_of_get_drdy_pin routine since of_property_read_u32
error conditions are already managed in st_lsm6dsx_get_drdy_reg()

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>