MIPS: ralink: Don't set pm_power_off

Setting pm_power_off is apprently wrong and makes drivers such as
gpio-poweroff not work.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11445/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>