proc: constify seq_operations

proc_uid_seq_operations, proc_gid_seq_operations and
proc_projid_seq_operations are only called in proc_id_map_open with
seq_open as const struct seq_operations so we can constify the 3
structures and update proc_id_map_open prototype.

   text    data     bss     dec     hex filename
   6817     404    1984    9205    23f5 kernel/user_namespace.o-before
   6913     308    1984    9205    23f5 kernel/user_namespace.o-after

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 2d696b0..79df9ff 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2449,7 +2449,7 @@
 
 #ifdef CONFIG_USER_NS
 static int proc_id_map_open(struct inode *inode, struct file *file,
-	struct seq_operations *seq_ops)
+	const struct seq_operations *seq_ops)
 {
 	struct user_namespace *ns = NULL;
 	struct task_struct *task;