ASoC: SOF: imx8: Fix an is IS_ERR() vs NULL check

The device_link_add() function only returns NULL on error, it doesn't
return error pointers.

Fixes: 202acc56 ("ASoC: SOF: imx: Add i.MX8 HW support")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NDaniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20190826131855.GA6840@mwandaSigned-off-by: NMark Brown <broonie@kernel.org>

sound/soc/sof/imx/imx8.c

@@ -227,8 +227,8 @@ static int imx8_probe(struct snd_sof_dev *sdev)
 						DL_FLAG_STATELESS |
 						DL_FLAG_PM_RUNTIME |
 						DL_FLAG_RPM_ACTIVE);
-		if (IS_ERR(priv->link[i])) {
-			ret = PTR_ERR(priv->link[i]);
+		if (!priv->link[i]) {
+			ret = -ENOMEM;
 			dev_pm_domain_detach(priv->pd_dev[i], false);
 			goto exit_unroll_pm;
 		}