glsl: Silence ignored qualifier warning
glsl: Silence ignored qualifier warning

I think the intention was to mark the "this" parameter as const, but
const goes on the other end to do that.

In file included from glsl_symbol_table.cpp:26:0:
ast.h:339:35: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
    const bool is_single_dimension()
                                   ^

Signed-off-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Reviewed-by: Timothy Arceri <5dd83789ef3714029244367ba1ca09f1d7627408@collabora.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler