nds32: Convert Makefiles to use COBJS-y style

Signed-off-by: Kuan-Yu Kuo <ken.kuoky@gmail.com>
Cc: Macpaul Lin <macpaul@gmail.com>
diff --git a/arch/nds32/cpu/n1213/Makefile b/arch/nds32/cpu/n1213/Makefile
index da15574..7e80082 100644
--- a/arch/nds32/cpu/n1213/Makefile
+++ b/arch/nds32/cpu/n1213/Makefile
@@ -31,8 +31,8 @@
 
 START	= start.o
 
-SRCS	:= $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS) $(SOBJS))
+SRCS	:= $(START:.o=.S) $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
+OBJS	:= $(addprefix $(obj),$(COBJS-y) $(SOBJS-y))
 START	:= $(addprefix $(obj),$(START))
 
 all:	$(obj).depend $(START) $(LIB)