drm_hwcomposer: Update the platform precompiler guards

Rename the guards in the platform headers to match their
filename. This wasn't done in the previous commits so the
diff remained clean.

BUG=b/28117135
TEST=compiles

Change-Id: Ie495bd8e00784da1d48f200c6981f23448b7c6d2
Signed-off-by: Sean Paul <seanpaul@chromium.org>
diff --git a/platformdrmgeneric.h b/platformdrmgeneric.h
index 8ea950c..3400876 100644
--- a/platformdrmgeneric.h
+++ b/platformdrmgeneric.h
@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_DRM_GENERIC_IMPORTER_H_
-#define ANDROID_DRM_GENERIC_IMPORTER_H_
+#ifndef ANDROID_PLATFORM_DRM_GENERIC_H_
+#define ANDROID_PLATFORM_DRM_GENERIC_H_
 
 #include "drmresources.h"
 #include "platform.h"