NFSv4: Fix a pNFS layout related use-after-free race when freeing the inode

NFSv4: Fix a pNFS layout related use-after-free race when freeing the inode

BugLink: https://bugs.launchpad.net/bugs/1910742
[ Upstream commit b6d49ecd1081740b6e632366428b960461f8158b ]

When returning the layout in nfs4_evict_inode(), we need to ensure that
the layout is actually done being freed before we can proceed to free the
inode itself.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>