[MIPS] IP22: Complain if requesting the front panel irq failed.

This fixes the warning:

  CC      arch/mips/sgi-ip22/ip22-reset.o
arch/mips/sgi-ip22/ip22-reset.c: In function 'reboot_setup':
arch/mips/sgi-ip22/ip22-reset.c:239: warning: ignoring return value of 'request_irq', declared with attribute warn_unused_result

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