sna: Limit the size of the tiling object to be smaller than either the originals

sna: Limit the size of the tiling object to be smaller than either the originals

When we tile, we do so in order to fit an operation involving two
objects larger than the aperture. If we then choose an intermediate
tiling object that is larger than either of those two, the error will
persist and we will be forced to recuse.

In the worst case, this will provide an upper bound to the recursion.

Reported-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>