Instead of manually coding the loop with of_find_node_by_type(), let's
switch to the standard macro for iterating over nodes with given type.

Also fixed a couple of refcount leaks in the aforementioned loops.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>