bcma: fix compile error

This error was introduced in:
commit e3f05a42
Author: Hauke Mehrtens <hauke@hauke-m.de>
Date:   Fri Jan 4 00:51:21 2013 +0100

    bcma: mips: explicit assign IRQ numbers

  CC      drivers/bcma/driver_mips.o
drivers/bcma/driver_mips.c: In function 'bcma_core_mips_init':
drivers/bcma/driver_mips.c:302:4: error: implicit declaration of
function 'bcma_core_irq' [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors
make[6]: *** [drivers/bcma/driver_mips.o] Error 1

Reported-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>