[media] exynos-gsc: don't release a non-dynamically allocated video_device

The struct v4l2_device instance for the G-Scaler is not dyanmically
allocated but a member of the struct gsc_dev. In fact, the assigned
.release callback is video_device_release_empty().

But gsc_register_m2m_device() attempts to release the v4l2_device by
calling video_device_release() in its error path. This is wrong since
the v4l2_device wasn't allocated directly and will be freed once its
parent struct gsc_dev is freed.

While being there, rename the remaining goto label in the error path
to something that better explains the error path cleanup.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>