[MIPS] rtlx: Fix build error.

  CC      arch/mips/kernel/rtlx.o
cc1: warnings being treated as errors
arch/mips/kernel/rtlx.c:59: warning: 'irq' defined but not used
arch/mips/kernel/rtlx.c:60: warning: 'irq_num' defined but not used

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