staging: line6: eliminate useless NULL checks

The line6 driver checks struct field addresses for NULL where it does
not make sense to do so.  The struct has already been checked for NULL
and there is no value in checking the first field's address too.

Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Markus Grabner <grabner@icg.tugraz.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>