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/DrmPlane.h b/drm/DrmPlane.h
index 31f0a33..c26a3cc 100644
--- a/drm/DrmPlane.h
+++ b/drm/DrmPlane.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_DRM_PLANE_H_
-#define ANDROID_DRM_PLANE_H_
+#pragma once
 
 #include <xf86drmMode.h>
 
@@ -100,5 +99,3 @@
   std::map<LayerTransform, uint64_t> transform_enum_map_;
 };
 }  // namespace android
-
-#endif  // ANDROID_DRM_PLANE_H_