i965/fs_nir: Turn on the peephole select optimization

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/mesa/drivers/dri/i965/brw_fs_nir.cpp

@@ -61,6 +61,8 @@ fs_visitor::emit_nir_code()
       nir_validate_shader(nir);
       nir_opt_dce(nir);
       nir_validate_shader(nir);
+      nir_opt_peephole_select(nir);
+      nir_validate_shader(nir);
       nir_print_shader(nir, stderr);
 
       nir_convert_from_ssa(nir);