drm_hwcomposer: Use pragma once instead of include guards

Some of existing include guards were copy-pasted without modification,
therefore have incorrect name. Switch to 'pragma once' in order to fix
it and avoid such copy-paste issues in the future.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/drm/VSyncWorker.h b/drm/VSyncWorker.h
index 1e6d39f..1774cc6 100644
--- a/drm/VSyncWorker.h
+++ b/drm/VSyncWorker.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_EVENT_WORKER_H_
-#define ANDROID_EVENT_WORKER_H_
+#pragma once
 
 #include <hardware/hardware.h>
 #include <hardware/hwcomposer.h>
@@ -55,5 +54,3 @@
   int64_t last_timestamp_ = -1;
 };
 }  // namespace android
-
-#endif