NFSv4: Fix an rcu lock leak

The intention in the original patch was to release the lock when
we put the inode, however something got screwed up.

Reported-by: Jason Yan <yanaijie@huawei.com>
Fixes: 7b410d9c ("pNFS: Delay getting the layout header in..")
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>