MAINTAINERS: update RBD block maintainer

Remove Josh as per his request since he is no longer the upstream RBD
tech lead. Add myself as the maintainer since I am the current RBD tech
lead.
Signed-off-by: NJason Dillaman <dillaman@redhat.com>
Reviewed-by: NJosh Durgin <jdurgin@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

MAINTAINERS

@@ -2385,7 +2385,7 @@ S: Supported
 F: block/vmdk.c
 
 RBD
-M: Josh Durgin <jdurgin@redhat.com>
+M: Jason Dillaman <dillaman@redhat.com>
 L: qemu-block@nongnu.org
 S: Supported
 F: block/rbd.c