ALSA: hdsp: silence a sprinft() overflow warning

card->shortname is a 32 char string so the sprintf() can theoretically
overflow.  snd_rawmidi_new() can accept strings up to 64 bytes long.

I have made the temporay buf[] array 40 bytes long and changed the
sprintf() to snprintf().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>