media: coda: move framebuffer size calculation out of loop

All internal YCbCr frame buffers are the same size, calculate ycbcr_size
once before the allocation loop.

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+samsung@kernel.org>