powerpc/sysdev: Add missing of_node_put()s

Add of_node_put() in various paths to drop references once they are no
longer needed.

Signed-off-by: Liang He <windhl@126.com>
[mpe: Rewrite change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220620130221.4073228-1-windhl@126.com