MAINTAINERS: Add qemu-img/io to block subsystem

qemu-img and qemu-io were not covered by any MAINTAINERS entry so far.
Reported-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

MAINTAINERS

@@ -674,6 +674,8 @@ S: Supported
 F: block*
 F: block/
 F: hw/block/
+F: qemu-img*
+F: qemu-io*
 T: git git://repo.or.cz/qemu/kevin.git block
 T: git git://github.com/stefanha/qemu.git block