Btrfs: only fua the first superblock when writting supers
Btrfs: only fua the first superblock when writting supers

We only intent to fua the first superblock in every device from
comments, fix it.

Signed-off-by: Wang Shilong <a6ffe7a539d70ea74089829fdeeb6c8d6acce33c@cn.fujitsu.com>
Signed-off-by: Josef Bacik <631dfb3d07694fdcf26abc7aac2c6c2b641f8bde@fb.com>
Signed-off-by: Chris Mason <e2e8c5702d8ed5f565988a1cf5bb35c9ce199e5e@fb.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs