Add clean target for data/ so make clean works again
diff --git a/data/Makefile b/data/Makefile
index bc57d23..0d57e96 100644
--- a/data/Makefile
+++ b/data/Makefile
@@ -16,6 +16,8 @@
 
 all :
 
+clean :
+
 install :
 	install -d $(datadir)/wayland
 	install $(cursor_images) $(datadir)/wayland