[ALSA] snd_hwdep_release() racefix

snd_card_file_remove() can free the snd_card.
Touch hw->* only before calling snd_card_file_remove().
Unrelated: Allow hwdep devices not to have own ops.release();

Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>