mn10300: add pci_get_legacy_ide_irq() to <asm/pci.h>

Add missing pci_get_legacy_ide_irq() implementation
before it becomes required by core IDE PCI code.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>