genirq: Fix type inconsistency

The return type of kstat_irqs_usr() is unsigned int and kstat_irqs() also
returns unsigned int so sum should be unsigned int here as well. 
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Link: http://lkml.kernel.org/r/1430642951-23964-1-git-send-email-hofrat@osadl.orgSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/irqdesc.c

@@ -639,7 +639,7 @@ unsigned int kstat_irqs(unsigned int irq)
  */
 unsigned int kstat_irqs_usr(unsigned int irq)
 {
-	int sum;
+	unsigned int sum;
 
 	irq_lock_sparse();
 	sum = kstat_irqs(irq);