Rebuild partition_table.img if src changes

Change-Id: Ic1c0112f360ec9ac9bcf601b2c1526f2c7f3e45f
diff --git a/partition-table.mk b/partition-table.mk
index b5426e5..fb7dfd6 100644
--- a/partition-table.mk
+++ b/partition-table.mk
@@ -6,7 +6,7 @@
 
 partition-table: $(PRODUCT_OUT)/partition-table.img
 
-$(PRODUCT_OUT)/partition-table.img:
+$(PRODUCT_OUT)/partition-table.img: $(ROOTDIR)/build/partition-table.bpt
 	mkdir -p $(PRODUCT_OUT)
 	$(ROOTDIR)/system/tools/bpt/bpttool make_table --input $(ROOTDIR)/build/partition-table.bpt --output_gpt $(PRODUCT_OUT)/partition-table.img