MIPS: ralink: add rt3883 wmac clock

Register the wireless mac clock on rti3883. This is required by the wifi driver.

Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/8007/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>