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/DrmFbImporter.h b/drm/DrmFbImporter.h
index 9e94238..9a7c335 100644
--- a/drm/DrmFbImporter.h
+++ b/drm/DrmFbImporter.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef DRM_DRMFBIMPORTER_H_
-#define DRM_DRMFBIMPORTER_H_
+#pragma once
 
 #include <drm/drm_fourcc.h>
 #include <hardware/gralloc.h>
@@ -87,5 +86,3 @@
 };
 
 }  // namespace android
-
-#endif