staging: line6: clean up line6_variax_process_message()

Previous versions of the line6 driver snooped MIDI traffic in order to
make device state accessible via sysfs attributes.  This involved a lot
of logic in line6_variax_process_message() that has since been removed.

Drop unused conditionals in line6_variax_process_message().

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>