staging: wilc1000: rename u8KeyLen in host_int_add_rx_gtk

This patch changes u8KeyLen to key_len to avoid camelcase.
It is used as local variable in order to save gtk_key_len that is
argument of this function.

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