pNFS: Don't clear the layout stateid if a layout return is outstanding

pNFS: Don't clear the layout stateid if a layout return is outstanding

commit 7b650994ab07434ae58a247dc9ac87d2488ca75c upstream.

If we no longer hold any layout segments, we're normally expected to
consider the layout stateid to be invalid. However we cannot assume this
if we're about to, or in the process of sending a layoutreturn.

Fixes: 334a8f37115b ("pNFS: Don't forget the layout stateid if...")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>