ALSA: line6: Fix POD sysfs attributes segfault

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()')
Cc: <stable@vger.kernel.org> # v4.0+
Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Andrej Krutak <dev@andree.sk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>