bcma: mips: fix clearing device IRQ

We were using wrong IRQ number so clearing wasn't working at all.
Depending on a platform this could result in a one device having two
interrupts assigned. On BCM4706 this resulted in all IRQs being broken.

Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: stable@vger.kernel.org
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>