1/ the return value of ldlm_resource_putref() is never
used, so change it to return 'void'.
2/ Move all of the code to run on the last putref to
__ldlm_resource_putref_final(). This means a lock
is taken in one function and dropped in another, but
that isn't too uncommon, and will disappear in a future
patch.
Now that the code it together, it becomes apparent that
we are dropping a ref on the namespace *before* the last
use. So keep the ref until after.