ALSA: core: Fix the debugfs removal at snd_card_free()

ALSA: core: Fix the debugfs removal at snd_card_free()

The commit 2d670ea2bd53 ("ALSA: jack: implement software jack
injection via debugfs") introduced a debugfs root for each sound card
object.  The debugfs entry gets removed at the card removal, too, but
it turned out that debugfs_remove() is called at a wrong place; it's
after the card object gets freed, hence it leads to use-after-free.

Fix it by moving the debugfs_remove() at the right place, the
destructor of the card device.

Fixes: 2d670ea2bd53 ("ALSA: jack: implement software jack injection via debugfs")
Reported-and-tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://lore.kernel.org/r/161228343605.1150.8862281636043446562@build.alporthouse.com
Link: https://lore.kernel.org/r/20210202225629.1965-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>