NFS: Unexport nfs_probe_fsinfo()

All the callers are now in client.c so we can remove the
EXPORT_SYMBOL_GPL() and make it static.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>