dpaa2-eth: Simplify the calculation of variables

Fix the following coccicheck warnings:

./drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c:1651:36-38: WARNING
!A || A && B is equivalent to !A || B.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Acked-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/1612260157-128026-1-git-send-email-jiapeng.chong@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c

@@ -1660,7 +1660,7 @@ void dpaa2_eth_set_rx_taildrop(struct dpaa2_eth_priv *priv,
 	 * CG taildrop threshold, so it won't interfere with it; we also
 	 * want frames in non-PFC enabled traffic classes to be kept in check)
 	 */
-	td.enable = !tx_pause || (tx_pause && pfc);
+	td.enable = !tx_pause || pfc;
 	if (priv->rx_cgtd_enabled == td.enable)
 		return;