powerpc/maple: Add missing of_node_put() in time.c

In maple_get_boot_time(), of_find_compatible_node() will return
a node pointer with refcount incremented. The reference should be
dropped with of_node_put() when it is not used anymore.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220617124045.4048757-1-windhl@126.com