proc: register filesystem last

As soon as register_filesystem() exits, filesystem can be mounted.  It
is better to present fully operational /proc.

Of course it doesn't matter because /proc is not modular but do it
anyway.

Drop error check, it should be handled by panicking.

Link: http://lkml.kernel.org/r/20180309222709.GA3843@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/root.c

@@ -123,14 +123,8 @@ static struct file_system_type proc_fs_type = {
 
 void __init proc_root_init(void)
 {
-	int err;
-
 	proc_init_kmemcache();
 	set_proc_pid_nlink();
-	err = register_filesystem(&proc_fs_type);
-	if (err)
-		return;
-
 	proc_self_init();
 	proc_thread_self_init();
 	proc_symlink("mounts", NULL, "self/mounts");
@@ -146,6 +140,8 @@ void __init proc_root_init(void)
 	proc_tty_init();
 	proc_mkdir("bus", NULL);
 	proc_sys_init();
+
+	register_filesystem(&proc_fs_type);
 }
 
 static int proc_root_getattr(const struct path *path, struct kstat *stat,