usr.sbin/makefs/ffs: Sync buf.c with FreeBSD

usr.sbin/makefs/ffs: Sync buf.c with FreeBSD

Bring in following FreeBSD commits,
while keeping DragonFly specific code for HAMMER2.

Note that msdosfs_vnops.c diff in FreeBSD e5551216d8e5 was never
merged to DragonFly makefs(8), so no need to apply (revert).

Sun Apr 16 15:45:17 2023 -0400 e5551216d8e5 makefs: call brelse from bread
Tue Apr 11 11:21:36 2023 -0400 af7624ed3145 makefs: use %s and __func__ in printf messages
Mon Apr 10 18:50:27 2023 -0400 1d1ffa2efd2a makefs: use size_t or ssize_t where appropriate