iio: common: ssp_sensors: gyro: use devm_iio_device_register()

Use devm_iio_device_register() for IIO subsystem device
registration and delete the remove function since there
is no need after this change.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>