nfsd: fix refcount leak when file is unhashed after being found

nfsd: fix refcount leak when file is unhashed after being found

[ Upstream commit 8a7926176378460e0d91e02b03f0ff20a8709a60 ]

If we wait_for_construction and find that the file is no longer hashed,
and we're going to retry the open, the old nfsd_file reference is
currently leaked. Put the reference before retrying.

Fixes: c6593366c0bf ("nfsd: don't kill nfsd_files because of lease break error")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Youzhong Yang <youzhong@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>