Fix struct vs. class mismatch in forward definitions

The warnings were being hidden by the use of -isystem to include
frameworks/native/include.

Bug: 31752268
Test: m -j
Change-Id: If2bae8b2fbc4238d6251cdd78bc7b5216684f99d
diff --git a/include/gui/SurfaceComposerClient.h b/include/gui/SurfaceComposerClient.h
index 312e02f..6c621ee 100644
--- a/include/gui/SurfaceComposerClient.h
+++ b/include/gui/SurfaceComposerClient.h
@@ -38,7 +38,7 @@
 
 // ---------------------------------------------------------------------------
 
-class DisplayInfo;
+struct DisplayInfo;
 class Composer;
 class HdrCapabilities;
 class ISurfaceComposerClient;