media: coda: fix frame_mem_ctrl for YUV420 and YVU420 formats

The frame memory control register value is currently determined
before userspace selects the final capture format and never corrected.
Update ctx->frame_mem_ctrl in __coda_start_decoding() to fix decoding
into YUV420 or YVU420 capture buffers.

Reported-by: Andrej Picej <andrej.picej@norik.com>
Fixes: 497e6b85 ("media: coda: add sequence initialization work")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>