drm/panfrost: Fix a BO leak in panfrost_ioctl_mmap_bo()

We should release the reference we grabbed when an error occurs.

Fixes: 187d2929 ("drm/panfrost: Add support for GPU heap allocations")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191129135908.2439529-4-boris.brezillon@collabora.com

drivers/gpu/drm/panfrost/panfrost_drv.c

@@ -303,14 +303,17 @@ static int panfrost_ioctl_mmap_bo(struct drm_device *dev, void *data,
 	}
 
 	/* Don't allow mmapping of heap objects as pages are not pinned. */
-	if (to_panfrost_bo(gem_obj)->is_heap)
-		return -EINVAL;
+	if (to_panfrost_bo(gem_obj)->is_heap) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	ret = drm_gem_create_mmap_offset(gem_obj);
 	if (ret == 0)
 		args->offset = drm_vma_node_offset_addr(&gem_obj->vma_node);
-	drm_gem_object_put_unlocked(gem_obj);
 
+out:
+	drm_gem_object_put_unlocked(gem_obj);
 	return ret;
 }