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/DrmUnique.h b/drm/DrmUnique.h
index 282528b..2be1eb9 100644
--- a/drm/DrmUnique.h
+++ b/drm/DrmUnique.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef DRM_UNIQUE_H_
-#define DRM_UNIQUE_H_
+#pragma once
 
 #include <xf86drmMode.h>
 
@@ -83,5 +82,3 @@
   return DrmModeResUnique(drmModeGetResources(fd),
                           [](drmModeRes *it) { drmModeFreeResources(it); });
 }
-
-#endif