brw: Get the reference to brw_def_analysis only once in saturate propagation

Instead of calling `require()` every instruction, call it once per pass.
Even though the defs are cached (i.e. we are not re-calculating them every
instruction), this prevents the extra check and the call to analysis
validation.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34010>
1 file changed