mips: ralink: fix a refcount leak in ill_acc_of_setup()

[ Upstream commit 4a0a1436053b17e50b7c88858fb0824326641793 ]

of_node_put(np) needs to be called when pdev == NULL.

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>