glsl: grammar fix
glsl: grammar fix

Signed-off-by: Eero Tamminen <c699dd7b5d663cbad4eb2e2f65c7464909a1c345@intel.com>
Reviewed-by: Eric Engestrom <de0b63cf2dfb1fae8ed3c3b4244856a05677d4f0@imgtec.com>
Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler