MIPS: lantiq: the detection of the gpe clock is broken

The code to detect unfused SoCs was broken due to missing register masking.

Signed-off-by: Thomas Langer <thomas.langer@lantiq.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/8049/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>