drm/xe/migrate: fix pat index usage

drm/xe/migrate: fix pat index usage

XE_CACHE_WB must be converted into the per-platform pat index for that
particular caching mode, otherwise we are just encoding whatever happens
to be the value of that enum.

Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241126181259.159713-3-matthew.auld@intel.com