ALSA: line6: Fix POD sysfs attributes segfault

commit b027d112 upstream.

The commit 02fc76f6 changed base of the sysfs attributes from device to card.
The "show" callbacks dereferenced wrong objects because of this.

Fixes: 02fc76f6 ('ALSA: line6: Create sysfs via snd_card_add_dev_attr()')
Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Andrej Krutak <dev@andree.sk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>