ARM: socfpga: Fix OF node refcount leak in SMP setup

ARM: socfpga: Fix OF node refcount leak in SMP setup

socfpga_smp_prepare_cpus() looks up the Cortex-A9 SCU node with
of_find_compatible_node(), which returns a node reference that must be
released with of_node_put().

The function maps the SCU registers and then returns without dropping
that reference, leaking the node on both the success path and the
of_iomap() failure path.

Drop the reference once the mapping attempt is complete. The returned
MMIO mapping does not depend on keeping the device node reference held.

Fixes: 122694a0c712 ("ARM: socfpga: use of_iomap to map the SCU")
Cc: stable@vger.kernel.org
Signed-off-by: Yuho Choi <dbgh9129@gmail.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>