staging: line6: Use explicit indexes when defining properties

Specify the index of the properties entry explicitly to define this
structure more robustly.  Also, drop the `L6PROP' macro in favor of
initializing each member explicitly on its own line since horizontal
space is limited and more attributes will be added later.

Signed-off-by: Chris Rorvick <chris@rorvick.com>
Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>