mips: ralink: Fix refcount leak in of.c

In plat_of_remap_node(), plat_of_remap_node() will return a node
pointer with refcount incremented. We should use of_node_put()
when it is not used anymore.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>