[IA64] pci_get_legacy_ide_irq should return irq (not GSI)

Function pci_get_legacy_ide_irq is incorrect on ia64. It should return
irq vector instead of GSI. The fixed number 14 and 15 are just GSI.

Signed-off-by: Zhang Yanmin <yanmin.zhang@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>