include/uapi/sound/asequencer.h: include sound/asound.h

Fixes userspace compilation error:
error: unknown type name ‘snd_seq_client_type_t’
snd_seq_client_type_t type; /* client type */

Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>