MAINTAINERS: add spdxexclude to LICENSES and SPDX stuff

Commit 0509b27 ("scripts/spdxcheck: Put excluded files and directories
into a separate file") moved excluded files to the new file
scripts/spdxexclude, but did not adjust the MAINTAINERS section. The file
scripts/spdxexclude clearly belongs to LICENSES and SPDX stuff.

Add a corresponding file entry.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20220825152029.12660-1-lukas.bulwahn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -11625,6 +11625,7 @@ F:	Documentation/process/license-rules.rst
 F:	LICENSES/
 F:	scripts/spdxcheck-test.sh
 F:	scripts/spdxcheck.py
+F:	scripts/spdxexclude
 
 LINEAR RANGES HELPERS
 M:	Mark Brown <broonie@kernel.org>