Revert "btrfs: use proper endianness accessors for super_copy"

This reverts commit 3c181c12 as it
causes breakage on big endian systems with btrfs images.

Reported-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Cc: Anand Jain <anand.jain@oracle.com>
Cc: Liu Bo <bo.li.liu@oracle.com>
Cc: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>