mips: cpc: Fix refcount leak in mips_cpc_default_phys_base

Add the missing of_node_put() to release the refcount incremented
by of_find_compatible_node().

Signed-off-by: Gong Yuanjun <ruc_gongyuanjun@163.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>