media: smiapp: Fix runtime PM imbalance on error

When v4l2_async_register_subdev_sensor_common() returns
an error code, a pairing runtime PM usage counter
decrement is needed to keep the counter balanced.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>