ARM: iop13xx: fix iq81340sc_atux_map_irq prototype

The pci map_irq callbacks get a 'const' pci_dev argument, so change the
iop13xx version to use the same prototype as everything else.

Without this patch, building iop13xx_defconfig results in:

arch/arm/mach-iop13xx/iq81340sc.c:63:2: warning: initialization from incompatible pointer type [enabled by default]
arch/arm/mach-iop13xx/iq81340sc.c:63:2: warning: (near initialization for 'iq81340sc_pci.map_irq') [enabled by default]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Dan Williams <djbw@fb.com>