Fix compilation error for MCF5275

Rename OBJ to COBJ in board/platform/Makefile

Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
diff --git a/board/freescale/m5275evb/Makefile b/board/freescale/m5275evb/Makefile
index f337a75..74c2528 100644
--- a/board/freescale/m5275evb/Makefile
+++ b/board/freescale/m5275evb/Makefile
@@ -25,7 +25,7 @@
 
 LIB	= $(obj)lib$(BOARD).a
 
-OBJS	= $(BOARD).o mii.o
+COBJS	= $(BOARD).o mii.o
 
 SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))