drm/i915: Mark up object tiling-and-stride getters as const

For that little bit of defense against a tired programmer.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180725155447.11909-1-chris@chris-wilson.co.uk
2 files changed