sh: Fix up rsk7203 target for out of tree build

Fix up rsk7203 target to build successfully using out-of-tree build.

Signed-off-by: Kieran Bingham <kbingham@mpc-data.co.uk>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/board/renesas/rsk7203/Makefile b/board/renesas/rsk7203/Makefile
index 7365d19..5412010 100644
--- a/board/renesas/rsk7203/Makefile
+++ b/board/renesas/rsk7203/Makefile
@@ -26,6 +26,10 @@
 OBJS	:= rsk7203.o
 SOBJS	:= lowlevel_init.o
 
+LIB	:= $(addprefix $(obj),$(LIB))
+OBJS	:= $(addprefix $(obj),$(OBJS))
+SOBJS	:= $(addprefix $(obj),$(SOBJS))
+
 $(LIB):	$(obj).depend $(OBJS) $(SOBJS)
 	$(AR) $(ARFLAGS) $@ $(OBJS) $(SOBJS)