Btrfs: Add 1MB to the min_free in alloc_chunk

	else

		min_free = calc_size;

	/* we add 1MB because we never use the first 1MB of the device */

	min_free += 1024 * 1024;

	/* build a private list of devices we will allocate from */

	while(index < num_stripes) {

		device = list_entry(cur, struct btrfs_device, dev_list);