LU-12514 obdclass: remove pointless struct lustre_mount_data2

LU-12514 obdclass: remove pointless struct lustre_mount_data2

This is used to pass a void* and NULL to lustre_fill_super().
It is easier just to pass the void*. The "NULL" passed is
sometimes a "struct vfsmount". This pointer is passed to
ll_fill_super() which then passes it to client_common_fill_super()
that just ignores it.

Linux-commit: 998831a00192a38a9f1425b2fb2d6faf3e34e665

Change-Id: If5e229d80c08b7c16e89d11a03fc766584c24f7c
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/35426
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>