md: constify VFTs

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -5976,7 +5976,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
 	return 0;
 }
 
-static struct seq_operations md_seq_ops = {
+static const struct seq_operations md_seq_ops = {
 	.start  = md_seq_start,
 	.next   = md_seq_next,
 	.stop   = md_seq_stop,