staging: vt6656: remove an unneeded NULL check

We dereference "param->u.wpa_key.key" on the next line so the check
here is inconsistent.  This is only called from iwctl_siwencodeext() and
"param->u.wpa_key.key" is a valid pointer.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>