makefs(8): Fix calculation of metadata segmets sizes

[kd]

Summary

• Remove "ncg" variable. It's always 1 and it was used to multiply stuff.

Adjust size calculations to match what is done in ffs_mkfs routine:

• Depending on the UFS version the superblock is stored at a different offset. Take that into account.
• Add the cylinder group block size.
• All of the above has to be aligned to the block size.

PR: 229929 (partially)

[mckusick]

Calculations and comment are accurate.