udf: convert byte order of constant instead of variable

convert byte order of constant instead of variable,
which can be done at compile time (vs run time)

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Acked-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>