x86/irq: Fix kbuild warning in smp_irq_move_cleanup_interrupt()

Fengguang Wu's 0day kernel build service reported the following build warning:

  arch/x86/kernel/apic/io_apic.c:2211
  smp_irq_move_cleanup_interrupt() warn: always true condition '(irq <= -1) => (0-u32max <= (-1))'

because irq is defined as an unsigned int instead of an int.
Fix this trivial error by redefining irq as a signed int.  The
remaining consumers of the int are okay.
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Link: http://lkml.kernel.org/r/1389620420-7110-1-git-send-email-prarit@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/apic/io_apic.c

@@ -2202,7 +2202,7 @@ asmlinkage void smp_irq_move_cleanup_interrupt(void)
 
 	me = smp_processor_id();
 	for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
-		unsigned int irq;
+		int irq;
 		unsigned int irr;
 		struct irq_desc *desc;
 		struct irq_cfg *cfg;