staging: wilc1000: rename u8Keyidx in host_int_add_wep_key_bss_sta

This patch changes u8Keyidx to index that is fourth argument of
host_int_add_wep_key_bss_sta to avoid camelcase.

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