iio:common: Set the device pointer into ST common sensors library

drivers/iio/accel/st_accel_i2c.c

drivers/iio/accel/st_accel_spi.c

drivers/iio/common/st_sensors/st_sensors_i2c.c

drivers/iio/common/st_sensors/st_sensors_spi.c

drivers/iio/gyro/st_gyro_i2c.c

drivers/iio/gyro/st_gyro_spi.c

drivers/iio/magnetometer/st_magn_i2c.c

drivers/iio/magnetometer/st_magn_spi.c

drivers/iio/pressure/st_pressure_i2c.c

drivers/iio/pressure/st_pressure_spi.c