drm/i915/ttm: fix static warning

warning: symbol 'i915_gem_ttm_obj_ops' was not declared. Should it be static?
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210623143411.293630-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -730,7 +730,7 @@ static u64 i915_ttm_mmap_offset(struct drm_i915_gem_object *obj)
 	return drm_vma_node_offset_addr(&obj->base.vma_node);
 }
 
-const struct drm_i915_gem_object_ops i915_gem_ttm_obj_ops = {
+static const struct drm_i915_gem_object_ops i915_gem_ttm_obj_ops = {
 	.name = "i915_gem_object_ttm",
 	.flags = I915_GEM_OBJECT_HAS_IOMEM,