nfs: Remove unused argument in nfs_server_set_fsinfo()

Commit e38eb650 "NFS: set_pnfs_layoutdriver() from nfs4_proc_fsinfo()"
have remove the using of mntfh from nfs_server_set_fsinfo().

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>