MIPS: Use current_cpu_type() instead of c->cputype

If current_cpu_type() is pre-defined in cpu-feature-overrides.h, This
may save about 10k for the compressed kernel image(vmlinuz).

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1901/


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