ALSA: cs46xx: Potential NULL dereference in probe

The "chip->dsp_spos_instance" can be NULL on some of the ealier error
paths in snd_cs46xx_create().

Reported-by: "Yavuz, Tuba" <tuba@ece.ufl.edu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>