staging: line6: drop unused line6_index and line6_id arrays

The line6 driver does not support 'index' and 'id' module parameters so
there is no need to keep arrays for these values.  Do what other sound
drivers do and use the scalar constants instead of dummy arrays.

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