btrfs: zoned: fix locking imbalance on scrub

If we're doing device replace on a zoned filesystem and discover in
scrub_enumerate_chunks() that we don't have to copy the block group it is
unlocked before it gets skipped.

But as the block group hasn't yet been locked before it leads to a locking
imbalance. To fix this simply remove the unlock.

This was uncovered by fstests' testcase btrfs/163.

Fixes: 9283b9e0 ("btrfs: remove lock protection for BLOCK_GROUP_FLAG_TO_COPY")
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -3911,7 +3911,6 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 
 		if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
 			if (!test_bit(BLOCK_GROUP_FLAG_TO_COPY, &cache->runtime_flags)) {
-				spin_unlock(&cache->lock);
 				btrfs_put_block_group(cache);
 				goto skip;
 			}