staging: wilc1000: rename WILC_WFI_add_station

This patch replaces WILC_WFI_add_station with add_station to avoid
CamelCase.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>