glsl: don't inline intrinsics for mediump

They have an empty fxn body, trying to handle them results in the
intrinsic call being expanded into a no-op.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6073>

src/compiler/glsl/lower_precision.cpp

@@ -883,6 +883,7 @@ find_precision_visitor::visit_enter(ir_call *ir)
     */
 
    if (!ir->callee->is_builtin() ||
+       ir->callee->is_intrinsic() ||
        return_var == NULL ||
        (return_var->data.precision != GLSL_PRECISION_MEDIUM &&
         return_var->data.precision != GLSL_PRECISION_LOW))