ASoC: wm_adsp: For TLV controls only register TLV get/set

Normal 512-byte get/set of a TLV isn't supported but we were
registering the normal get/set anyway and relying on omitting
the SNDRV_CTL_ELEM_ACCESS_[READ|WRITE] flags to prevent them
being called.

Trouble is if this gets broken in the core ALSA code - as it has
been since at least 4.14 - the standard get/set can be called
unexpectedly and corrupt memory.

There's no point providing functions that won't be called and
it's a trivial change. The benefit is that if the ALSA core gets
broken again we get a big fat immediate NULL dereference instead
of a memory corruption timebomb.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

sound/soc/codecs/wm_adsp.c

@@ -1204,12 +1204,14 @@ static int wmfw_add_ctl(struct wm_adsp *dsp, struct wm_coeff_ctl *ctl)
 		kcontrol->put = wm_coeff_put_acked;
 		break;
 	default:
-		kcontrol->get = wm_coeff_get;
-		kcontrol->put = wm_coeff_put;
-
+		if (kcontrol->access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK) {
 			ctl->bytes_ext.max = ctl->len;
 			ctl->bytes_ext.get = wm_coeff_tlv_get;
 			ctl->bytes_ext.put = wm_coeff_tlv_put;
+		} else {
+			kcontrol->get = wm_coeff_get;
+			kcontrol->put = wm_coeff_put;
+		}
 		break;
 	}