LU-12514 obdclass: remove vfsmount option from client_fill_super

LU-12514 obdclass: remove vfsmount option from client_fill_super

This arg is always NULL and is never used.
So discard it from this and related functions.

Linux-commit: 7dc2155195586ec75f53d6dcd381f935ccc35d02

Change-Id: I00b16115edbff0de7605768121981b928585552c
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/35427
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>