include/uapi/sound/emu10k1.h: include sound/asound.h

Fixes userspace compilation errors like:
error: field ‘id’ has incomplete type
struct snd_ctl_elem_id id;  /* full control ID definition */

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