media: mediatek: vcodec: Correct vsi_core framebuffer size

The framebuffer size for decoder instances was being incorrectly set -
inst->vsi_core->fb.y.size was assigned twice consecutively.

Assign the second picinfo framebuffer size to the C framebuffer instead,
which appears to be the intended target based on the surrounding code.

Fixes: 2674486a ("media: mediatek: vcodec: support stateless hevc decoder")
Cc: stable@vger.kernel.org
Signed-off-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>