media: coda: reduce minimum frame size to 48x16 pixels.

Three macroblocks seem to be the minimum resolution that can be encoded
and decoded by the CODA960 h.264 codec. Picture run commands fail for
smaller resolutions.

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>