sched/headers: Add header guard to kernel/sched/sched.h

Use the canonical header guard naming of the full path to the header.

Signed-off-by: Ingo Molnar <[e-mail]>
Reviewed-by: Peter Zijlstra <[e-mail]>

kernel/sched/sched.h

···
 /*
  * Scheduler internal types and methods:
  */
+#ifndef _KERNEL_SCHED_SCHED_H
+#define _KERNEL_SCHED_SCHED_H
+
 #include <linux/sched.h>
 
 #include <linux/sched/autogroup.h>
···
 extern void sched_dynamic_update(int mode);
 #endif
 
+#endif /* _KERNEL_SCHED_SCHED_H */