bcm47xx: Fix warning

arch/mips/bcm947xx/irq.c: In function 'pcibios_map_irq':
arch/mips/bcm947xx/irq.c:78: warning: passing argument 1 of 'pci_name' discards qualifiers from pointer target type


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@10626 3c298f89-4303-0410-b956-a3cf2f4a3e73