powerpc/cell/axon_msi: Fix refcount leak in setup_msi_msg_address

of_get_next_parent() returns a node pointer with refcount incremented,
we should use of_node_put() on it when not need anymore.
Add missing of_node_put() in the error path to avoid refcount leak.

Fixes: ce21b3c9

 ("[CELL] add support for MSI on Axon-based Cell systems")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220605065129.63906-1-linmq006@gmail.com