libblkid: udf: Correctly handle UDF strings encoded in 8bit OSTA Compressed Unicode

libblkid: udf: Correctly handle UDF strings encoded in 8bit OSTA Compressed Unicode

String encoded in 8bit OSTA Compressed Unicode contains one Unicode
codepoint per 8bits. Maximal Unicode codepoint is U+FF. Which effectively
means that it is equivalent to Latin1 encoding.

Before this patch libblkid copied raw 8bit OSTA Compressed Unicode from
disk and treated it as UTF-8. It worked fine just for UTF-8 invariants,
other characters were incorrectly encoded. This patch fixes this problem.

Note that processing UUID is not fixed in this patch.