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: Abaci Robot <[e-mail]>
Signed-off-by: Jiapeng Chong <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/xen-netfront.c

···
 	 *  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)