media: platform: mtk-mdp3: release node reference before returning

The iterator for_each_child_of_node() increments the refcount of the
child node it is processing. Release such a reference when the loop
needs to break due to an error during its execution.
Issue identified using for_each_child.cocci Coccinelle semantic patch.

Signed-off-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>