st/mesa: fix up result_src.type when doing i2u/u2i conversions

Even though it's a no-op, it's important to keep track of the type so
that we can pick the properly-signed op later on.

This fixes dEQP-GLES3.functional.shaders.precision.uint.highp_div_fragment,
which ended up using IDIV instead of UDIV.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit 49c67926c7)

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -1935,6 +1935,7 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
    case ir_unop_u2i:
       /* Converting between signed and unsigned integers is a no-op. */
       result_src = op[0];
+      result_src.type = result_dst.type;
       break;
    case ir_unop_b2i:
       if (native_integers) {