fs/nsfs.c: include headers for missing declarations

Include linux/proc_fs.h and fs/internal.h to address the following
'sparse' warnings:

fs/nsfs.c:41:32: warning: symbol 'ns_dentry_operations' was not declared. Should it be static?
fs/nsfs.c:145:5: warning: symbol 'open_related_ns' was not declared. Should it be static?

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Eric Biggers <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/nsfs.c

···
 #include <linux/pseudo_fs.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/proc_fs.h>
 #include <linux/proc_ns.h>
 #include <linux/magic.h>
 #include <linux/ktime.h>
···
 #include <linux/user_namespace.h>
 #include <linux/nsfs.h>
 #include <linux/uaccess.h>
+
+#include "internal.h"
 
 static struct vfsmount *nsfs_mnt;