media: coda: store unmasked fifo position in meta

Storing the unmasked kfifo->in position as meta->start and ->end allows
to more easily compare a point past meta->end with the current
kfifo->in.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>