MAINTAINERS: add include files to virtio-serial entry

Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>

MAINTAINERS

@@ -696,6 +696,7 @@ M: Amit Shah <amit.shah@redhat.com>
 S: Supported
 F: hw/char/virtio-serial-bus.c
 F: hw/char/virtio-console.c
+F: include/hw/virtio/virtio-serial.h
 
 virtio-rng
 M: Amit Shah <amit.shah@redhat.com>