media: vimc: handle error in vimc_add_subdevs

In case the 'add' callback of an entity fails,
then all other entities should unregister and released.
This should be done inside vimc_add_subdevs so that
the function handles its own failure.

In order to call vimc_unregister_subdevs and vimc_release_subdevs from
vimc_add_subdevs, the order of the function should change.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>