nand_spl: fix u-boot.lst breakage

Commit 97b24d3d51a92cb8c0c1e1a74abf22fe1a1807a3 "common: Add symbol
handling for generic lists into Makefile" introduced build errors in many
nand_spl targets, complaining of a missing u-boot.lst.  When not doing an
out-of-tree build, $(obj) expands to nothing, so GCC ended up being given
-I with no argument (or rather, -ansi was the argument).  The failure
didn't show up during a -j1 build because it was picking up the non-SPL
version of u-boot.lst.

Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/nand_spl/board/freescale/mpc8536ds/Makefile b/nand_spl/board/freescale/mpc8536ds/Makefile
index e5388d8..822ae7c 100644
--- a/nand_spl/board/freescale/mpc8536ds/Makefile
+++ b/nand_spl/board/freescale/mpc8536ds/Makefile
@@ -67,7 +67,8 @@
 # $(LDSCRIPT). The function make_u_boot_list is defined in helper.mk file.
 $(eval $(call make_u_boot_list, $(LSTSCRIPT), $(OBJS)))
 $(nandobj)u-boot-nand_spl.lds: $(LDSCRIPT) $(LSTSCRIPT)
-	$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -I$(obj) -ansi -D__ASSEMBLY__ -P - <$< >$@
+	$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -I$(nandobj)/board/$(BOARDDIR) \
+		-ansi -D__ASSEMBLY__ -P - <$< >$@
 
 # create symbolic links for common files