drm/tegra: falcon: Fix error handling

The ->alloc() callback in struct falcon_ops returns an ERR_PTR()-encoded
error code on failure, so it needs to be properly checked for, otherwise
subsequent code may dereference an invalid pointer.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/falcon.c

@@ -141,9 +141,9 @@ int falcon_load_firmware(struct falcon *falcon)
 	/* allocate iova space for the firmware */
 	falcon->firmware.vaddr = falcon->ops->alloc(falcon, firmware->size,
 						    &falcon->firmware.paddr);
-	if (!falcon->firmware.vaddr) {
-		dev_err(falcon->dev, "dma memory mapping failed\n");
-		return -ENOMEM;
+	if (IS_ERR(falcon->firmware.vaddr)) {
+		dev_err(falcon->dev, "DMA memory mapping failed\n");
+		return PTR_ERR(falcon->firmware.vaddr);
 	}
 
 	/* copy firmware image into local area. this also ensures endianness */