Makefile: fix bug introduced by commit 47ffd6c2
diff --git a/common/Makefile b/common/Makefile
index d3888d6..8d4a426 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -153,7 +153,7 @@
 COBJS-$(CONFIG_USB_KEYBOARD) += usb_kbd.o
 COBJS-$(CONFIG_DDR_SPD) += ddr_spd.o
 
-COBJS	:= $(sort COBJS-y)
+COBJS	:= $(sort $(COBJS-y))
 SRCS	:= $(AOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(AOBJS) $(COBJS))