[media] pwc: switch to the new auto-cluster volatile handling

Now that the auto cluster core changed to a different scheme of how to
handle volatile controls (including how to switch from auto to manual mode)
the pwc code can be simplified to use that new core support.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>