MAINTAINERS: add David as additional tcg/s390 maintainer

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index e3e0b1d..54feb95 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -236,6 +236,7 @@
 S390
 M: Richard Henderson <rth@twiddle.net>
 M: Alexander Graf <agraf@suse.de>
+M: David Hildenbrand <david@redhat.com>
 S: Maintained
 F: target/s390x/
 F: hw/s390x/