NFS: Convert __nfs_revalidate_inode() to use nfs_refresh_inode()

In the case where there are parallel RPC calls to the same inode, we may
receive stale metadata due to the lack of ordering, hence the sanity
checking of metadata in nfs_refresh_inode().
Currently, __nfs_revalidate_inode() is calling nfs_update_inode() directly,
without any further sanity checks, and hence may end up setting the inode
up with stale metadata.

Fix is to use nfs_refresh_inode() instead of nfs_update_inode().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>