radv: skip updating depth/color metadata for conditional rendering

I don't think we should update metadata when conditional rendering
is enabled. For some reasons, some CTS breaks only on SI.

This fixes the following CTS on SI:
dEQP-VK.conditional_rendering.draw_clear.clear.depth.*

Cc: 19.0 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit 6596eb2b)