seq_file: constify seq_operations

Make all seq_operations structs const, to help mitigate against
revectoring user-triggerable function pointers.

This is derived from the grsecurity patch, although generated from scratch
because it's simpler than extracting the changes from there.

Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/mn10300/kernel/setup.c

@@ -285,7 +285,7 @@ static void c_stop(struct seq_file *m, void *v)
 {
 }
 
-struct seq_operations cpuinfo_op = {
+const struct seq_operations cpuinfo_op = {
 	.start	= c_start,
 	.next	= c_next,
 	.stop	= c_stop,