media: ti-vpe: cal: Share buffer release code between start and stop

The cal_start_streaming() and cal_stop_streaming() functions duplicate
the same buffer release logic. split it to a separate function to share
the code.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>