mixer: Fix missing hctl handle free in snd_mixer_attach_hctl()
mixer: Fix missing hctl handle free in snd_mixer_attach_hctl()

Yet another missing piece.

Also, update the function document to warn about the behavior at
error.

Signed-off-by: Takashi Iwai <4596b3305151c7ee743192a95d394341e3d3b644@suse.de>

alsa-project/alsa-lib,mengdonglin/alsa-lib,lgirdwood/alsa-lib,mengdonglin/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,lgirdwood/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,zedongchen/alsa-lib,mengdonglin/alsa-lib,zedongchen/alsa-lib,mengdonglin/alsa-lib,Distrotech/alsa-lib,alsa-project/alsa-lib,zedongchen/alsa-lib,Distrotech/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,tiwai/alsa-lib,Distrotech/alsa-lib,takaswie/alsa-lib,lgirdwood/alsa-lib,lgirdwood/alsa-lib,alsa-project/alsa-lib,zedongchen/alsa-lib,Distrotech/alsa-lib,Distrotech/alsa-lib,mengdonglin/alsa-lib,tiwai/alsa-lib,zedongchen/alsa-lib,lgirdwood/alsa-lib