staging: wilc1000: change join_req_drv type and it's name

To use wilc_get_vif_idx instead of the last get_id_from_handler, join_req_drv
needs to be changed it's type with wilc_vif and name as well.
As a result, get_id_from_handler is not used anymore, so remove it.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>