RFC: fix to build issue with subdirs

Pushing this to see what fails as its a similar fix to the one Flavio
pushed.  Yet in local building with sanitytest not seeing any issues

Change-Id: If42c13b0c1827fe89fb332ac6c40a14a76553330
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 0494a88..6924cb1 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -176,7 +176,7 @@
 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
 # Usage:
 # $(Q)$(MAKE) $(build)=dir
-build := -f $(srctree)/scripts/Makefile.build obj
+build := -f $(ZEPHYR_BASE)/scripts/Makefile.build obj
 
 ###
 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.modbuiltin obj=