drm/tegra: Use unlocked gem unreferencing

For drm_gem_object_unreference callers are required to hold
dev->struct_mutex, which these paths don't. Enforcing this requirement
has become a bit more strict with

commit ef4c6270
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Oct 15 09:36:25 2015 +0200

    drm/gem: Check locking in drm_gem_object_unreference

Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/drm.c

@@ -473,7 +473,7 @@ static int tegra_gem_mmap(struct drm_device *drm, void *data,
 
 	args->offset = drm_vma_node_offset_addr(&bo->gem.vma_node);
 
-	drm_gem_object_unreference(gem);
+	drm_gem_object_unreference_unlocked(gem);
 
 	return 0;
 }
@@ -683,7 +683,7 @@ static int tegra_gem_set_tiling(struct drm_device *drm, void *data,
 	bo->tiling.mode = mode;
 	bo->tiling.value = value;
 
-	drm_gem_object_unreference(gem);
+	drm_gem_object_unreference_unlocked(gem);
 
 	return 0;
 }
@@ -723,7 +723,7 @@ static int tegra_gem_get_tiling(struct drm_device *drm, void *data,
 		break;
 	}
 
-	drm_gem_object_unreference(gem);
+	drm_gem_object_unreference_unlocked(gem);
 
 	return err;
 }
@@ -748,7 +748,7 @@ static int tegra_gem_set_flags(struct drm_device *drm, void *data,
 	if (args->flags & DRM_TEGRA_GEM_BOTTOM_UP)
 		bo->flags |= TEGRA_BO_BOTTOM_UP;
 
-	drm_gem_object_unreference(gem);
+	drm_gem_object_unreference_unlocked(gem);
 
 	return 0;
 }
@@ -770,7 +770,7 @@ static int tegra_gem_get_flags(struct drm_device *drm, void *data,
 	if (bo->flags & TEGRA_BO_BOTTOM_UP)
 		args->flags |= DRM_TEGRA_GEM_BOTTOM_UP;
 
-	drm_gem_object_unreference(gem);
+	drm_gem_object_unreference_unlocked(gem);
 
 	return 0;
 }