hw/xen: Avoid use of uninitialized bufioreq_evtchn

Avoid use of uninitialized bufioreq_evtchn. It should only
be used if buffered IOREQs are enabled.

Resolves: Coverity CID 1563383
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>

hw/xen/xen-hvm-common.c

@@ -752,9 +752,10 @@ static int xen_map_ioreq_server(XenIOState *state)
         return -1;
     }
 
-    trace_xen_map_ioreq_server_buffered_io_evtchn(bufioreq_evtchn);
-
-    state->bufioreq_remote_port = bufioreq_evtchn;
+    if (state->has_bufioreq) {
+        trace_xen_map_ioreq_server_buffered_io_evtchn(bufioreq_evtchn);
+        state->bufioreq_remote_port = bufioreq_evtchn;
+    }
 
     return 0;
 }