NFSv4/pnfs: pnfs_set_layout_stateid() should update the layout cred

[ Upstream commit 59b5639490f51aa604d18064dcf0c2d72eb1decf ]

If the cred assigned to the layout that we're updating differs from
the one used to retrieve the new layout segment, then we need to
update the layout plh_lc_cred field.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Stable-dep-of: 6d6d7f91cc8c ("NFSv4/pnfs: Reset the layout state after a layoutreturn")
Signed-off-by: Sasha Levin <sashal@kernel.org>