btrfs: use temporary variable for space_info in btrfs_update_block_group

We do

  cache->space_info->counter += num_bytes;

everywhere in here.  This is makes the lines longer than they need to
be, and will be especially noticeable when we add the active tracking in,
so add a temp variable for the space_info so this is cleaner.
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -3476,6 +3476,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans,
 	spin_unlock(&info->delalloc_root_lock);
 
 	while (total) {
+		struct btrfs_space_info *space_info;
 		bool reclaim = false;
 
 		cache = btrfs_lookup_block_group(info, bytenr);
@@ -3483,6 +3484,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans,
 			ret = -ENOENT;
 			break;
 		}
+		space_info = cache->space_info;
 		factor = btrfs_bg_type_to_factor(cache->flags);
 
 		/*
@@ -3497,7 +3499,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans,
 		byte_in_group = bytenr - cache->start;
 		WARN_ON(byte_in_group > cache->length);
 
-		spin_lock(&cache->space_info->lock);
+		spin_lock(&space_info->lock);
 		spin_lock(&cache->lock);
 
 		if (btrfs_test_opt(info, SPACE_CACHE) &&
@@ -3510,24 +3512,24 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans,
 			old_val += num_bytes;
 			cache->used = old_val;
 			cache->reserved -= num_bytes;
-			cache->space_info->bytes_reserved -= num_bytes;
-			cache->space_info->bytes_used += num_bytes;
-			cache->space_info->disk_used += num_bytes * factor;
+			space_info->bytes_reserved -= num_bytes;
+			space_info->bytes_used += num_bytes;
+			space_info->disk_used += num_bytes * factor;
 			spin_unlock(&cache->lock);
-			spin_unlock(&cache->space_info->lock);
+			spin_unlock(&space_info->lock);
 		} else {
 			old_val -= num_bytes;
 			cache->used = old_val;
 			cache->pinned += num_bytes;
-			btrfs_space_info_update_bytes_pinned(info,
-					cache->space_info, num_bytes);
-			cache->space_info->bytes_used -= num_bytes;
-			cache->space_info->disk_used -= num_bytes * factor;
+			btrfs_space_info_update_bytes_pinned(info, space_info,
+							     num_bytes);
+			space_info->bytes_used -= num_bytes;
+			space_info->disk_used -= num_bytes * factor;
 
 			reclaim = should_reclaim_block_group(cache, num_bytes);
 
 			spin_unlock(&cache->lock);
-			spin_unlock(&cache->space_info->lock);
+			spin_unlock(&space_info->lock);
 
 			set_extent_dirty(&trans->transaction->pinned_extents,
 					 bytenr, bytenr + num_bytes - 1,