powerpc/cell: Add missing of_node_put()s

Use of_node_put() for of_find_node_by_path() and
of_find_node_by_phandle() to keep refcount balance.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220619072335.4067728-1-windhl@126.com