nfsd: fix nfsdfs inode reference count leak

nfsd: fix nfsdfs inode reference count leak

BugLink: https://bugs.launchpad.net/bugs/1886995
[ Upstream commit bf2654017e0268cc83dc88d56f0e67ff4406631d ]

I don't understand this code well, but  I'm seeing a warning about a
still-referenced inode on unmount, and every other similar filesystem
does a dput() here.

Fixes: e8a79fb14f6b ("nfsd: add nfsd/clients directory")
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>