Cleanup out-or-tree building for some boards (.depend)

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/r7780mp/Makefile b/board/r7780mp/Makefile
index 34ce9a8..0ab6d1d 100644
--- a/board/r7780mp/Makefile
+++ b/board/r7780mp/Makefile
@@ -36,7 +36,7 @@
 	rm -f $(SOBJS) $(OBJS)
 
 distclean:	clean
-	rm -f $(LIB) core *.bak .depend
+	rm -f $(LIB) core *.bak $(obj).depend
 
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