rcu: Fix mismatched variable in rcutree_trace.c

rcutree.c defines rcu_cpu_kthread_cpu as int, not unsigned int,
so the extern has to follow that.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree_trace.c

@@ -49,7 +49,7 @@
 #ifdef CONFIG_RCU_BOOST
 
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
+DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DECLARE_PER_CPU(char, rcu_cpu_has_work);