Kbuild: Makefile.modbuiltin: include auto.conf and tristate.conf mandatory

The files auto.conf and tristate.conf are mandatory for building
modules.builtin files, therefore include them as such.

Usually, the top-level Makefile ensures that those files exist but we
want to make sure we get noticed if they are missing for whatever
reason.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/Makefile.modbuiltin b/scripts/Makefile.modbuiltin
index 40867a4..a072a42 100644
--- a/scripts/Makefile.modbuiltin
+++ b/scripts/Makefile.modbuiltin
@@ -8,10 +8,10 @@
 PHONY := __modbuiltin
 __modbuiltin:
 
--include include/config/auto.conf
+include include/config/auto.conf
 # tristate.conf sets tristate variables to uppercase 'Y' or 'M'
 # That way, we get the list of built-in modules in obj-Y
--include include/config/tristate.conf
+include include/config/tristate.conf
 
 include scripts/Kbuild.include