sysutils/openzfs*: Bump to fix build

This updates the ports to bc8192cd5 and fixes the sysutils/openzfs
build after openzfs/zfs#13316 overhauled the build system.

The update also fixes the sysutils/openzfs-kmod build errors for
unused-but-set-variable warnings, which have been corrected upstream.

Approved by: lwhsu (implicit)
Sponsored by: iXsystems, Inc.