staging: wilc1000: rename au8bssid in struct join_bss_param

This patch renames au8bssid to bssid to remove au8 prefix in struct
join_bss_param. There is no need to use prefix to show data type of this
variable.

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