iris: Reorder the loops in iris_fence_await() for clarity.

iris: Reorder the loops in iris_fence_await() for clarity.

Swapping the order of the loops makes the logic much easier to follow:
for each point in our fence, if it hasn't gone by, make future work in
all batches depend on it.  Both loops are necessary, and now it's
clearer why.

(This doesn't actually fix a bug but needs to be cherry-picked for
the next patch to apply, which does fix a bug.)

Fixes: f459c56be6b ("iris: Add fence support using drm_syncobj")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Tapani Pälli <tapani.palli@intel.com>
Tested-by: Yang A Shi <yang.a.shi@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6463>