drm/mediatek: fix potential OF node use-after-free

In the Linux kernel, the following vulnerability has been resolved:

drm/mediatek: fix potential OF node use-after-free

The for_each_child_of_node() helper drops the reference it takes to each node as it iterates over children and an explicit of_node_put() is only needed when exiting the loop early.

Drop the recently introduced bogus additional reference count decrement at each iteration that could potentially lead to a use-after-free.