gallium/swr: Fix array stride problem.

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>
Tested-by: Marge Bot <mesa/mesa!4405>
Part-of: <mesa/mesa!4405>
23 jobs for !4405 with swr-fix-array-stride in 13 minutes and 18 seconds (queued for 5 seconds)
merge request