media: Revert "media: cedrus: Allow using the current dst buffer as reference"

This reverts commit cf20ae15.

The vb2_find_timestamp helper was modified to allow finding buffers
regardless of their current state in the queue. This means that we
no longer have to take particular care of references to the current
capture buffer.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>