libblkid: use blkid_probe_open_device() in evaluate and verify

Convert evaluate.c and verify.c to use blkid_probe_open_device()
instead of open() + blkid_probe_set_device(). This makes these
internal callers VFS-aware and simplifies fd ownership.

Clean up verify.c error paths with dev_err/dev_free labels.

Signed-off-by: Karel Zak <kzak@redhat.com>