staging: rtl8188eu: fix rtw_xmit_entry's return value

A netdev xmit function should return NETDEV_TX_OK or NETDEV_TX_BUSY.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210122165749.29467-1-martin@kaiser.cxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/os_dep/xmit_linux.c

@@ -205,5 +205,5 @@ int rtw_xmit_entry(struct sk_buff *pkt, struct net_device *pnetdev)
 		 ("%s: drop, tx_drop=%d\n", __func__, (u32)pxmitpriv->tx_drop));
 
 exit:
-	return 0;
+	return NETDEV_TX_OK;
 }