media: rkvdec: Fix a NULL vs IS_ERR() bug in probe()

The iommu_paging_domain_alloc() function doesn't return NULL on error it
returns error pointers.  Update the check and then set ->empty_domain to
NULL because the rest of the driver assumes it can be NULL.

Fixes: ff8c562 ("media: rkvdec: Restore iommu addresses on errors")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Tested-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

Author: Dan Carpenter

drivers/media/platform/rockchip/rkvdec/rkvdec.c

@@ -1162,8 +1162,10 @@ static int rkvdec_probe(struct platform_device *pdev)
 	if (iommu_get_domain_for_dev(&pdev->dev)) {
 		rkvdec->empty_domain = iommu_paging_domain_alloc(rkvdec->dev);
 
-		if (!rkvdec->empty_domain)
+		if (IS_ERR(rkvdec->empty_domain)) {
+			rkvdec->empty_domain = NULL;
 			dev_warn(rkvdec->dev, "cannot alloc new empty domain\n");
+		}
 	}
 
 	vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32));