After iterating the children of a node with for_each_child_of_node(),
the child node will never be NULL. If the node was not found,
overlay_child will always point to the first element in the list, which
might or might not be the node that was searched.

Use the of_get_child_by_name() helper function to find the child node
with the name, which does the right thing and returns NULL if the node
is not found.

Reported-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>