mips: ralink: add missing of_node_put() call in ill_acc_of_setup()

of_find_compatible_node() takes a reference to the device_node
which needs to be dropped when done.

Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>