glsl/distance: make sure we use clip dist varying slot for lowered var.

When lowering, we always want to use the clip dist varying.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/compiler/glsl/lower_distance.cpp

@@ -168,6 +168,7 @@ lower_distance_visitor::visit(ir_variable *ir)
       *new_var = ir->clone(ralloc_parent(ir), NULL);
       (*new_var)->name = ralloc_strdup(*new_var, GLSL_CLIP_VAR_NAME);
       (*new_var)->data.max_array_access = new_size - 1;
+      (*new_var)->data.location = VARYING_SLOT_CLIP_DIST0;
 
       if (!ir->type->fields.array->is_array()) {
          /* gl_ClipDistance (used for vertex, tessellation evaluation and