Don't overwrite useful message when creating macvlan fails

Currently we report a bogus error message when macvlan
creation fails:

error: Failed to start domain migtest
error: operation failed: Unable to create macvlan device

With this removed, we see the real error:

error: Failed to start domain migtest
error: Unable to get index for interface p31p1: No such device
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/util/virnetdevmacvlan.c

@@ -897,11 +897,8 @@ create_name:
         }
 
         virMutexUnlock(&virNetDevMacVLanCreateMutex);
-        if (!cr_ifname) {
-            virReportError(VIR_ERR_OPERATION_FAILED, "%s",
-                           _("Unable to create macvlan device"));
+        if (!cr_ifname)
             return -1;
-        }
     }
 
     if (virNetDevVPortProfileAssociate(cr_ifname,