drm/ttm: drop extra ttm_bo_put in ttm_bo_cleanup_refs

That was accidentially left over when we switched to the delayed delete
worker.

Suggested-by: Matthew Auld <matthew.william.auld@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 9bff18d1

 ("drm/ttm: use per BO cleanup workers")
Reported-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230316072647.406707-1-christian.koenig@amd.com