nouveau_drm_load() calls pm_runtime_put() if nouveau_runtime_pm != 0,
but nouveau_drm_unload() calls pm_runtime_get_sync() unconditionally.
We therefore leak a runtime pm ref whenever nouveau is loaded with
runpm=0 and then unloaded. The GPU will subsequently never runtime
suspend even if nouveau is loaded again with runpm=1.
Fix by taking the runtime pm ref under the same condition that it was
released on driver load.