udf: Use device size when drive reported bogus number of written blocks

commit 24a5d59f upstream.

Some drives report 0 as the number of written blocks when there are some blocks
recorded. Use device size in such case so that we can automagically mount such
media.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>