staging: vt6655: wpactl.c: Fix sparse warnings

Add missing __user macro casting in the function wpa_set_keys.
This is okay since the function handles the possibility of
param->u.wpa_key.key and param->u.wpa_key.seq pointing to
kernelspace using a flag, fcpfkernel.

Signed-off-by: Martin Berglund <martin@rogsta.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>