MIPS: ath79: fix a wrong IRQ number

MIPS: ath79: fix a wrong IRQ number

The Ubiquiti XM board setup code uses an invalid
IRQ number, because it if above of NR_IRQS. This
leads to failed 'request_irq' calls:

  ath9k 0000:00:00.0: request_irq failed
  ath9k: probe of 0000:00:00.0 failed with error -22

Preserve some IRQ numbers for the built-in IRQ
controller of PCI host controllers in the
AR71XX/AR724X SoCs, and use the correct IRQ
number in the board setup code.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3495/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>