s390/qeth: remove useless if/else

Fix the following coccinelle report:

./drivers/s390/net/qeth_l3_main.c:107:2-4: WARNING: possible condition with no effect (if == else)

Both branches are the same since
commit ab29c480 ("s390/qeth: replace deprecated simple_stroul()"),
so remove them.

Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
[jwi: point to the commit that introduced this]
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>