xtensa: iss: drop opened_list logic from the network driver

xtensa: iss: drop opened_list logic from the network driver

opened_list is used to poll all opened devices in the timer callback,
but there's individual timer that is associated with each device.
Drop opened_list and only poll the device that is associated with the
timer in the timer callback.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>