usr.sbin/makefs: Sync with sys/vfs/hammer2

usr.sbin/makefs: Sync with sys/vfs/hammer2

Sync with following sys/vfs/hammer2 commits.

$ git log --pretty="%h %s" e49cd5358c56593a7923a00706d26dbc4e8bdaed.. -- sys/vfs/hammer2/
d6f11ef8ed sys/vfs/hammer2: Remove unneeded (char *)bp->b_data cast
0a7ab00601 sys/vfs/hammer2: Comment out unused local variables
8fd12ec463 sys/vfs/hammer2: Remove KKASSERT expecting path to start with "/dev/"
2e3d3c15cd sys/vfs/hammer2: Use HAMMER2_ROOT_VOLUME instead of 0
9be1b0c77a Revert "sys/vfs/hammer2: Avoid void* pointer arithmetic"