btrfs: split write_dev_supers to two functions

There are two independent parts, one that writes the superblocks and
another that waits for completion. No functional changes, but cleanups,
reformatting and comment updates.

Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2017-06-16 00:50:33 +02:00
commit abbb3b8ebf