btrfs: initialize btrfs_delayed_ref_head with btrfs_ref

btrfs: initialize btrfs_delayed_ref_head with btrfs_ref

We are calling init_delayed_ref_head with all of the elements from
btrfs_ref, clean this up to simply pass in the btrfs_ref and initialize
the btrfs_delayed_ref_head with the values from the btrfs_ref directly.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>