xtensa: iss: fix handling error cases in iss_net_configure()

The 'pdev' and 'netdev' need to be released in error cases of
iss_net_configure().

Change the return type of iss_net_configure() to void, because it's
not used.

Fixes: 7282bee7

 ("[PATCH] xtensa: Architecture support for Tensilica Xtensa Part 8")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>