v3dv: fix subpass tracking in the command buffer state

When we create a new job for a new subpass, we might have to finish
the current job for the previous subpass, so it is important that we
we don't get ahead of ourselves and increment the current subpass index
in the command buffer state until we are really done finishing the
previous job.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
3 files changed