cbfstool: Proper commonlib include path with no dependency on $(src)

$(src) is not defined when building directly from the cbfs directory (that is,
when building cbfs as standalone, running make in the cbfs directory), so we
need to define the path to the commonlib include path relative to $(top).

Change-Id: I72e80b030d4a156ec653ded5ab1457b16f612526
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-on: http://review.coreboot.org/11706
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)
diff --git a/util/cbfstool/Makefile.inc b/util/cbfstool/Makefile.inc
index 0938ea9..a1dbfc3 100644
--- a/util/cbfstool/Makefile.inc
+++ b/util/cbfstool/Makefile.inc
@@ -50,7 +50,7 @@
 TOOLCPPFLAGS += -I$(top)/util/cbfstool/flashmap
 TOOLCPPFLAGS += -I$(top)/util/cbfstool
 TOOLCPPFLAGS += -I$(objutil)/cbfstool
-TOOLCPPFLAGS += -I$(src)/commonlib/include
+TOOLCPPFLAGS += -I$(top)/src/commonlib/include
 TOOLLDFLAGS ?=
 
 ifeq ($(shell uname -s | cut -c-7 2>/dev/null), MINGW32)