exfat: convert to simple_rename_timestamp

A rename potentially involves updating 4 different inode timestamps.
Convert to the new simple_rename_timestamp helper function.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Message-Id: <20230705190309.579783-10-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>