glsl: Add fp16 case for ir_triop_lrp optimization

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3929>

src/compiler/glsl/opt_algebraic.cpp

@@ -983,6 +983,9 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
          ir_constant *one;
 
          switch (ir->type->base_type) {
+         case GLSL_TYPE_FLOAT16:
+            one = new(mem_ctx) ir_constant(float16_t::one(), op2_components);
+            break;
          case GLSL_TYPE_FLOAT:
             one = new(mem_ctx) ir_constant(1.0f, op2_components);
             break;