btrfs: calculate the right space for delayed refs when updating global reserve

commit f8f210dc upstream.

When updating the global block reserve, we account for the 6 items needed
by an unlink operation and the 6 delayed references for each one of those
items. However the calculation for the delayed references is not correct
in case we have the free space tree enabled, as in that case we need to
touch the free space tree as well and therefore need twice the number of
bytes. So use the btrfs_calc_delayed_ref_bytes() helper to calculate the
number of bytes need for the delayed references at
btrfs_update_global_block_rsv().

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[Diogo: this patch has been cherry-picked from the original commit;
conflicts included lack of a define (picked from commit 5630e2bc)
and lack of btrfs_calc_delayed_ref_bytes (picked from commit 0e55a545)
- changed const struct -> struct for compatibility.]
Signed-off-by: Diogo Jahchan Koike <djahchankoike@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>