NFS: Don't skip directory entries when doing uncached readdir

NFS: Don't skip directory entries when doing uncached readdir

BugLink: https://bugs.launchpad.net/bugs/1963889
[ Upstream commit ce292d8faf41f62e0fb0c78476c6fce5d629235a ]

Ensure that we initialise desc->cache_entry_index correctly in
uncached_readdir().

Fixes: d1bacf9eb2fd ("NFS: add readdir cache array")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>