media: mediatek: vcodec: change lat thread decode error condition

If lat thread can't get lat buffer, it should be that current instance
don't be schedulded, the driver can't free the src buffer directly.

Fixes: 7b182b8d ("media: mediatek: vcodec: Refactor get and put capture buffer flow")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>