glsl: No longer require ubo block index to be constant in ir_validate

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ir_validate.cpp

@@ -495,7 +495,6 @@ ir_validate::visit_leave(ir_expression *ir)
       break;
 
    case ir_binop_ubo_load:
-      assert(ir->operands[0]->as_constant());
       assert(ir->operands[0]->type == glsl_type::uint_type);
 
       assert(ir->operands[1]->type == glsl_type::uint_type);