glsl_to_tgsi: reduce the size of st_dst_reg and st_src_reg

I noticed that glsl_to_tgsi_instruction is too huge.

sizeof(glsl_to_tgsi_instruction): 752 -> 464 (-38%)

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
1 file changed