btrfs: simplify the bioc argument for handle_ops_on_dev_replace()

There is no memory re-allocation for handle_ops_on_dev_replace(), thus
we don't need to pass a btrfs_io_context pointer.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>