LU-6142 lustre: change all 'struct seq_operations' to const

LU-6142 lustre: change all 'struct seq_operations' to const

All 'struct seq_operations' are now 'static const'.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ia0f6a2863835ec02fb7d283a099eea489f65ab3a
Reviewed-on: https://review.whamcloud.com/39396
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>