namespace: Use atomic64_inc_return() in alloc_mnt_ns()

Use atomic64_inc_return(&ref) instead of atomic64_add_return(1, &ref)
to use optimized implementation and ease register pressure around
the primitive for targets that implement optimized variant.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20241007085303.48312-1-ubizjak@gmail.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: ubizjak

fs/namespace.c

@@ -3901,7 +3901,7 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
 	}
 	new_ns->ns.ops = &mntns_operations;
 	if (!anon)
-		new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
+		new_ns->seq = atomic64_inc_return(&mnt_ns_seq);
 	refcount_set(&new_ns->ns.count, 1);
 	refcount_set(&new_ns->passive, 1);
 	new_ns->mounts = RB_ROOT;