libblkid: udf: Fix reporting UDF 2.60 revision

libblkid: udf: Fix reporting UDF 2.60 revision

According to the UDF 2.60 specification, the Minimum UDF Read Revision
value shall be at most #0250 for all media with a UDF 2.60 file system.

So in this case use Minimum UDF Write Revision as ID_FS_VERSION to
distinguish between UDF 2.50 and UDF 2.60 discs.

This commit also adds a testing Blu-Ray Recordable image with UDF revision
2.60 created by Nero which really sets Minimum UDF Read Revision to 2.50.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>