staging: wilc1000: use TAG_PARAM_OFFSET define

TAG_PARAM_OFFSET is defined at top of this file so that it is used
to simplify codes.

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