MAINTAINERS: add virtio-ccw.h to virtio/s390 section

The file arch/s390/include/uapi/asm/virtio-ccw.h belongs to the
s390 virtio drivers as well.
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

MAINTAINERS

@@ -14312,6 +14312,7 @@ L:	virtualization@lists.linux-foundation.org
 L:	kvm@vger.kernel.org
 S:	Supported
 F:	drivers/s390/virtio/
+F:	arch/s390/include/uapi/asm/virtio-ccw.h
 
 VIRTIO GPU DRIVER
 M:	David Airlie <airlied@linux.ie>