RFR: 8303749: Serial: Use more strict card table API

[Albert Mingkun Yang]

On Tue, 7 Mar 2023 13:29:50 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple refactoring to skip an unnecessary guard check.
> 
> Test: tier1-3

Thanks for the review.

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PR: https://git.openjdk.org/jdk/pull/12902