mips: mti-malta: Fix refcount leak in malta-time.c

In update_gic_frequency_dt(), of_find_compatible_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>