radeonsi: rename members of si_shader_output_values
radeonsi: rename members of si_shader_output_values

Be a bit more verbose and avoid confusion in future patches.

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler