powerpc/85xx: Add missing of_node_put() in ksi8560.c

In ksi8560_setup_arch(), 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/20220616132922.3987053-1-windhl@126.com