Applying § 1322(e) and Puerto Rico law, 10% “penalty clause” in mortgage was subject to equitable reduction from $7,600 to $2,000. “[Section] 1322(e) controls the determination of the amount of pre-petition attorney’s fees which may be included in a secured creditor’s mortgage arrearage claim. . . . [Section] 1322(e) permits recovery of attorney’s fees and expenses only if allowed by applicable nonbankruptcy law. . . . [P]enal clauses in Puerto Rico are ‘subject to the principle of moderation’ under Puerto Rico law.”