mesa: set GLSL 1.20 for the fixed-function fragment shader
mesa: set GLSL 1.20 for the fixed-function fragment shader

This fixes broken depth texturing after:

commit 22639a6e19f95902aef23474ad672bf489231ea7
Author: Timothy Arceri <timothy.arceri@collabora.com>
Date:   Mon Nov 21 00:29:29 2016 +1100

    st/mesa: get Version from gl_program rather than gl_shader_program

Reviewed-by: Roland Scheidegger <7d58aee419d6f9201d75517c885374dff5e7d848@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler