staging: line6: drop tuner param filtering

The pod_set_system_param_int() helper function is only used to set the
monitor level.  Previously it was also used to control the tuner and has
special checks.  These checks can now be dropped, along with the tuner
constants.

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