makefs: call brelse from bread

This matches NetBSD and rationalizes makefs with the kernel API.

This reverts commit 370e009188ba90c3290b1479aa06ec98b66e140a.

Reviewed by: mckusick
Sponsored by: The FreeBSD Foundation
Obtained from: NetBSD 0a62dad69f62, 0c4125e1a19f, cb6a5a3575fd
Differential Revision: https://reviews.freebsd.org/D39070

(cherry picked from commit e5551216d8e563043248bc7f3cb1c75b2dbd9791)