genirq: Fix the return type of kstat_cpu_irqs_sum()

The type of member ->irqs_sum is unsigned long, but kstat_cpu_irqs_sum()
returns int, which can result in truncation.  Therefore, change the
kstat_cpu_irqs_sum() function's return value to unsigned long to avoid
truncation.

Fixes: f2c66cd8 ("/proc/stat: scalability of irq num per cpu")
Reported-by: Elliott, Robert (Servers) <elliott@hpe.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Josh Don <joshdon@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

include/linux/kernel_stat.h

@@ -75,7 +75,7 @@ extern unsigned int kstat_irqs_usr(unsigned int irq);
 /*
  * Number of interrupts per cpu, since bootup
  */
-static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
+static inline unsigned long kstat_cpu_irqs_sum(unsigned int cpu)
 {
 	return kstat_cpu(cpu).irqs_sum;
 }