drm/tegra: vic: Fix DMA API misuse

Upon failure, dma_alloc_coherent() returns NULL. If that does happen,
passing some uninitialised stack contents to dma_mapping_error() - which
belongs to a different API in the first place - has precious little
chance of detecting it.

Also include the correct header, because the fragile transitive
inclusion currently providing it is going to break soon.

Fixes: 20e7dce2 ("drm/tegra: Remove memory allocation from Falcon library")
CC: Thierry Reding <thierry.reding@gmail.com>
CC: Mikko Perttunen <mperttunen@nvidia.com>
CC: dri-devel@lists.freedesktop.org
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/vic.c

@@ -5,6 +5,7 @@
 
 #include <linux/clk.h>
 #include <linux/delay.h>
+#include <linux/dma-mapping.h>
 #include <linux/host1x.h>
 #include <linux/iommu.h>
 #include <linux/module.h>
@@ -232,10 +233,8 @@ static int vic_load_firmware(struct vic *vic)
 
 	if (!client->group) {
 		virt = dma_alloc_coherent(vic->dev, size, &iova, GFP_KERNEL);
-
-		err = dma_mapping_error(vic->dev, iova);
-		if (err < 0)
-			return err;
+		if (!virt)
+			return -ENOMEM;
 	} else {
 		virt = tegra_drm_alloc(tegra, size, &iova);
 	}