Add package source as a dependency of the deb

- We depend on the debian metadata, but not actually the source code ;)

Change-Id: Icb7a8ece06d7c5bdfad0158424bf49ed13fd99bf
diff --git a/packages.mk b/packages.mk
index 577cf47..1fd1da6 100644
--- a/packages.mk
+++ b/packages.mk
@@ -57,6 +57,7 @@
 $(PRODUCT_OUT)/.$1-pbuilder: \
 	$(foreach package,$3,$(PRODUCT_OUT)/.$(package)-pbuilder) \
 	$(shell find $(ROOTDIR)/packages/$1 -type f) \
+	$(shell find $(ROOTDIR)/$2 -type f) \
 	| $(ROOTDIR)/cache/base.tgz \
 	$4