MAINTAINERS: add Benjamin Marzinski as a device mapper maintainer

Ben will be working with me as a maintainer, so add him to the
MAINTAINERS file.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Mike Snitzer <snitzer@kernel.org>

Author: Mikulas Patocka

MAINTAINERS

@@ -7123,6 +7123,7 @@ DEVICE-MAPPER  (LVM)
 M:	Alasdair Kergon <agk@redhat.com>
 M:	Mike Snitzer <snitzer@kernel.org>
 M:	Mikulas Patocka <mpatocka@redhat.com>
+M:	Benjamin Marzinski <bmarzins@redhat.com>
 L:	dm-devel@lists.linux.dev
 S:	Maintained
 Q:	http://patchwork.kernel.org/project/dm-devel/list/