drivers: net: xen-netfront: Simplify the calculation of variables

Fix the following coccicheck warnings:

./drivers/net/xen-netfront.c:1816:52-54: WARNING !A || A && B is
equivalent to !A || B.
Reported-by: NAbaci Robot <abaci@linux.alibaba.com>
Signed-off-by: NJiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: NJuergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/1612261069-13315-1-git-send-email-jiapeng.chong@linux.alibaba.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>

drivers/net/xen-netfront.c

@@ -1811,7 +1811,7 @@ static int setup_netfront(struct xenbus_device *dev,
 	 *  a) feature-split-event-channels == 0
 	 *  b) feature-split-event-channels == 1 but failed to setup
 	 */
-	if (!feature_split_evtchn || (feature_split_evtchn && err))
+	if (!feature_split_evtchn || err)
 		err = setup_netfront_single(queue);
 
 	if (err)