sched: fix signedness warnings in sched.c

Unsigned long values are always assigned to switch_count,
make it unsigned long.

kernel/sched.c:3897:15: warning: incorrect type in assignment (different signedness)
kernel/sched.c:3897:15:    expected long *switch_count
kernel/sched.c:3897:15:    got unsigned long *<noident>
kernel/sched.c:3921:16: warning: incorrect type in assignment (different signedness)
kernel/sched.c:3921:16:    expected long *switch_count
kernel/sched.c:3921:16:    got unsigned long *<noident>

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -3889,7 +3889,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev)
 asmlinkage void __sched schedule(void)
 {
 	struct task_struct *prev, *next;
-	long *switch_count;
+	unsigned long *switch_count;
 	struct rq *rq;
 	int cpu;