nfs: fix duplicate proc entries

nfs: fix duplicate proc entries

commit 2f3169fb18f4643ac9a6a097a6a6c71f0b2cef75 upstream.

Commit 65b38851a174
("NFS: Fix /proc/fs/nfsfs/servers and /proc/fs/nfsfs/volumes")

updated the following function:
static int nfs_volume_list_open(struct inode *inode, struct file *file)

it used &nfs_server_list_ops instead of &nfs_volume_list_ops
which means cat /proc/fs/nfsfs/volumes = /proc/fs/nfsfs/servers

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Fixes: 65b38851a174 (NFS: Fix /proc/fs/nfsfs/servers and...)
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>