drm/sched: Fix preprocessor guard

When writing the header guard for gpu_scheduler_trace.h, a typo,
apparently, occurred.

Fix the typo and document the scope of the guard.

Fixes: 353da3c ("drm/amdgpu: add tracepoint for scheduler (v2)")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218124149.118002-2-phasta@kernel.org

Author: Philipp Stanner

drivers/gpu/drm/scheduler/gpu_scheduler_trace.h

@@ -21,7 +21,7 @@
  *
  */
 
-#if !defined(_GPU_SCHED_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#if !defined(_GPU_SCHED_TRACE_H_) || defined(TRACE_HEADER_MULTI_READ)
 #define _GPU_SCHED_TRACE_H_
 
 #include <linux/stringify.h>
@@ -106,7 +106,7 @@ TRACE_EVENT(drm_sched_job_wait_dep,
 		      __entry->seqno)
 );
 
-#endif
+#endif /* _GPU_SCHED_TRACE_H_ */
 
 /* This part must be outside protection */
 #undef TRACE_INCLUDE_PATH