intel/eu: Set message subtype properly for SIMD8 FB fetch

There were two bugs which crep in here as part of 64551610d1e6:
forgetting that exec sizes in HW are in log2 space and having the
exec_size condition for the subtype backwards.

Fixes: 64551610d1e6 "intel/compiler: rework message descriptors..."
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10588>
2 files changed