xen: Use evtchn_type_t as a type for event channels

Make event channel functions pass event channel port using
evtchn_port_t type. It eliminates signed <-> unsigned conversion.

Signed-off-by: Yan Yankovskyi <yyankovskyi@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20200323152343.GA28422@kbp1-lhp-F74019
Signed-off-by: Juergen Gross <jgross@suse.com>
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index ba0942e..75c0a2e 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -854,7 +854,8 @@ static int scsiback_init_sring(struct vscsibk_info *info, grant_ref_t ring_ref,
 static int scsiback_map(struct vscsibk_info *info)
 {
 	struct xenbus_device *dev = info->dev;
-	unsigned int ring_ref, evtchn;
+	unsigned int ring_ref;
+	evtchn_port_t evtchn;
 	int err;
 
 	err = xenbus_gather(XBT_NIL, dev->otherend,