surfaceflinger: Make all sources depend on Android.mk

This forces all SurfaceFlinger sources to be recompiled when the
Makefile changes; that's overkill sometimes but makes sure everything
gets recompiled when compile options (or similar) changes.

Change-Id: I2b3c3090fc1c35078e13c77fbb1a78d447c39158
diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index 888d2f8..f279491 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -3,6 +3,7 @@
 
 LOCAL_CLANG := true
 
+LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk
 LOCAL_SRC_FILES:= \
     Client.cpp \
     DisplayDevice.cpp \