brw: Use the right width in brw_nir_apply_key for BS shaders

Fixes: 23c7142cd67 ("anv: disable SIMD16 for RT shaders")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35798>
1 file changed