udf: Convert ident strings to proper charset

iocharset= mount option specifies the character set used on *console*
(not on disk). So even dstrings from VRS need to be converted from CS0
to the specified charset and not always UTF-8. This is barely user
visible as those strings are shown only in UDF debug messages.

CC: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Signed-off-by: Jan Kara <jack@suse.cz>