Makefile: support running graph-depends from out-of-tree

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
diff --git a/Makefile b/Makefile
index 6faa698..7624f59 100644
--- a/Makefile
+++ b/Makefile
@@ -647,7 +647,8 @@
 
 graph-depends:
 	@$(INSTALL) -d $(O)/graphs
-	@./support/scripts/graph-depends \
+	@cd "$(CONFIG_DIR)"; \
+	$(TOPDIR)/support/scripts/graph-depends \
 	|dot -T$(BR2_GRAPH_OUT) -o $(O)/graphs/$(@).$(BR2_GRAPH_OUT)
 
 else # ifeq ($(BR2_HAVE_DOT_CONFIG),y)