gcc 4.2 warns

linux/arch/i386/kernel/io_apic.c: In function ‘create_irq’:
linux/arch/i386/kernel/io_apic.c:2488: warning: ‘vector’ may be used uninitialized in this function

The warning is false, but somewhat legitimate so work around it.
Signed-off-by: Andi Kleen <ak@suse.de>