Btrfs: call the ordered free operation without any locks held

Btrfs: call the ordered free operation without any locks held

commit e9fbcb42201c862fd6ab45c48ead4f47bb2dea9d upstream.

Each ordered operation has a free callback, and this was called with the
worker spinlock held.  Josef made the free callback also call iput,
which we can't do with the spinlock.

This drops the spinlock for the free operation and grabs it again before
moving through the rest of the list.  We'll circle back around to this
and find a cleaner way that doesn't bounce the lock around so much.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>