rtl8139: using CP_TX_OWN for ownership transferring during tx

Through CP_TX_OWN and CP_RX_OWN points to the same bit, we'd better use
CP_TX_OWN for tx descriptor handling.

Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/rtl8139.c

@@ -2046,7 +2046,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
     }
 
     /* transfer ownership to target */
-    txdw0 &= ~CP_RX_OWN;
+    txdw0 &= ~CP_TX_OWN;
 
     /* reset error indicator bits */
     txdw0 &= ~CP_TX_STATUS_UNF;