[IA64] Fix possible invalid memory access in ia64_setup_msi_irq()

The following 'if' statement in ia64_setup_msi_irq() always fails even
if create_irq() returns <0 value, because variable 'irq' is defined as
unsigned int. It would cause invalid memory access.

        irq = create_irq();
        if (irq < 0)
                return irq;

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>