i965/miptree: Use the correct BLT pitch

Retile miptrees to a linear tiling less often. Retiling can cause issues
with imported BOs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106738


Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
(cherry picked from commit 0288fe8d)