Fix fallthrough warning

Fix a single fallthrough warning and re-enable -Wimplicit-fallthrough.

Test: m libhwui
Change-Id: I850f53f717417f70c9d0416176d03fd64473d1ba
diff --git a/libs/hwui/HardwareBitmapUploader.cpp b/libs/hwui/HardwareBitmapUploader.cpp
index 9bb6031..b64588e 100644
--- a/libs/hwui/HardwareBitmapUploader.cpp
+++ b/libs/hwui/HardwareBitmapUploader.cpp
@@ -302,6 +302,7 @@
     switch (skBitmap.info().colorType()) {
         case kRGBA_8888_SkColorType:
             formatInfo.isSupported = true;
+            [[fallthrough]];
         // ARGB_4444 is upconverted to RGBA_8888
         case kARGB_4444_SkColorType:
             formatInfo.pixelFormat = PIXEL_FORMAT_RGBA_8888;