staging: wilc1000: rename u8security in wilc_set_join_req

This patch renames u8security to security to remove u8 prefix.
There is no need to add prefix in order 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>