Align with the block size of overlayBD

[salvete]

What this PR does / why we need it:

The inconsistency in the default block sizes between OverlayBD and EROFS can lead to issues during segment mapping. This patch aligns with the block size of overlaybd for mapping (i.e., OverlayBD's 512-byte size) to overcome this inconsistency.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Please check the following list:

• [ ] Does the affected code have corresponding tests, e.g. unit test, E2E test?
• [ ] Does this change require a documentation update?
• [ ] Does this introduce breaking changes that would require an announcement or bumping the major version?
• [ ] Do all new files have an appropriate license header?

[BigVan]

@hsiangkao PLTAL

[BigVan]

thanks