Report correct error in virNetDevTapCreate

ioctl returns -1, not the errno value

src/util/virnetdevtap.c

@@ -294,7 +294,7 @@ int virNetDevTapCreate(char **ifname,
         }
 
         if ((flags & VIR_NETDEV_TAP_CREATE_PERSIST) &&
-            (errno = ioctl(fd, TUNSETPERSIST, 1))) {
+            ioctl(fd, TUNSETPERSIST, 1) < 0) {
             virReportSystemError(errno,
                                  _("Unable to set tap device %s to persistent"),
                                  NULLSTR(*ifname));