Recalculate buffer checksums. Uses flags.
On entry, EAX contains sector size for this block
On entry, ESI contains the cache block handle.
This routine will compute a sector by sector checksum of a buffer's contents and save the sums for later verification by calling VCache_VerifySums. An FSD should recalculate the checksums whenever the contents of a buffer are change but the buffer is not going to be made dirty. EG: by reading data into the buffer.