isBlockAligned to use uint64_t

We want to avoid the usage of size_t for any integer value that could
exceed 2^32 (for 32 bit platforms). Let's update the usage here for
future compatibilty and avoid silent truncation failures.

Bug: 361048795
Test: th
Change-Id: I9ce2ca21706270a218f06f7d2b7dc9fade185a68