MAINTAINERS: Add scripts/clang-tools to Kbuild section

Masahiro has always applied scripts/clang-tools patches but it is not
included in the Kbuild section, so neither he nor linux-kbuild get cc'd
on patches that touch those files.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>