exfat: ensure that ctime is updated whenever the mtime is

When removing entries from a directory, the ctime must also be updated
alongside the mtime.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Message-Id: <20230705190309.579783-4-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>