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 <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
1 file changed