[media] coda: fix mvcol buffer for MPEG4 decoding

The mvcol buffer is allocated at the end of the first internal buffer.
This patch fixes an out of bounds array access.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>