radv: fix HTILE metadata initialization in presence of subpass clears

If the driver ends up by performing a slow depthstencil clear,
the HTILE metadata won't be initialized correctly.

This fixes random VM faults on Polaris while running CTS
with Bas's runner. This doesn't seem to regress performance.

CC: <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 07cb1373)