i965/miptree: Use the tiling from the modifier instead of the BO

This fixes a bug where we were taking the tiling from the BO regardless
of what the modifier said.  When we got images in from Vulkan where it
doesn't set the tiling on the BO, we would treat them as linear even
though the modifier expressly said to treat it as Y-tiled.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit ad424b22)