fix out of tree building with kallsyms

The call to SYSTEM_MAP assumes that the u-boot output is in $PWD when
it really should be in $(obj).  This fixes building out of tree.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Makefile

@@ -517,7 +517,7 @@ $(obj)u-boot:	depend \
 		$(SUBDIR_TOOLS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds
 		$(GEN_UBOOT)
 ifeq ($(CONFIG_KALLSYMS),y)
-		smap=`$(call SYSTEM_MAP,u-boot) | \
+		smap=`$(call SYSTEM_MAP,$(obj)u-boot) | \
 			awk '$$2 ~ /[tTwW]/ {printf $$1 $$3 "\\\\000"}'` ; \
 		$(CC) $(CFLAGS) -DSYSTEM_MAP="\"$${smap}\"" \
 			-c common/system_map.c -o $(obj)common/system_map.o