soundwire: intel_init: test link->cdns

intel_link_probe() could return error and dev_get_drvdata() will return
null in such case. So we have to test link->cdns after
link->cdns = dev_get_drvdata(&ldev->auxdev.dev);
Otherwise, we will meet the "kernel NULL pointer dereference" error.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210406010101.11442-1-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/intel_init.c

@@ -178,6 +178,15 @@ static struct sdw_intel_ctx
 		link->pdev = pdev;
 		link->cdns = platform_get_drvdata(pdev);
 
+		if (!link->cdns) {
+			dev_err(&adev->dev, "failed to get link->cdns\n");
+			/*
+			 * 1 will be subtracted from i in the err label, but we need to call
+			 * intel_link_dev_unregister for this ldev, so plus 1 now
+			 */
+			i++;
+			goto err;
+		}
 		list_add_tail(&link->list, &ctx->link_list);
 		bus = &link->cdns->bus;
 		/* Calculate number of slaves */