[POWERPC] Fix unbalanced uses of of_node_put

The (maple|pasemi)_init_IRQ functions call of_node_put(root) once more
than they should, causing the refcount of the root node to underflow,
which triggers the WARN_ON in kref_get.

Signed-off-by: Nathan Lynch <ntl@pobox.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>