libgui: Only allow one return from useFenceSync

An #ifdef was causing multiple returns in this function, which was
triggering an unreachable code error on some build targets. This
adds an #else to ensure that only one return is exposed in any given
build.

Change-Id: I9ed7c3e769bc9094ad31d810944227d1d8302886

libs/gui/SyncFeatures.cpp

@@ -77,10 +77,11 @@ bool SyncFeatures::useFenceSync() const {
     // on some devices it's better to not use EGL_KHR_fence_sync
     // even if they have it
     return false;
-#endif
+#else
     // currently we shall only attempt to use EGL_KHR_fence_sync if
     // USE_FENCE_SYNC is set in our makefile
     return !mHasNativeFenceSync && mHasFenceSync;
+#endif
 }
 bool SyncFeatures::useWaitSync() const {
     return (useNativeFenceSync() || useFenceSync()) && mHasWaitSync;