radv: Flush before vkCmdWriteTimestamp() if needed

As done for vkCmdBeginQuery() already. Prevents timestamps from being
overwritten by previous vkCmdResetQueryPool() calls if the shader path
was used to do the reset.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108925


Fixes: a41e2e9c ("radv: allow to use a compute shader for resetting the query pool")
Signed-off-by: Alex Smith <asmith@feralinteractive.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit c1b6cb06)
[Juan A. Suarez: resolve trivial conflicts]
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>

Conflicts:
	src/amd/vulkan/radv_query.c