Staging: line6: depends on SND

line6 code has lots of dependencies on ALSA (and build errors),
so express that in Kconfig.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Markus Grabner <grabner@icg.tugraz.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>