btrfs: switch btrfs_block_group::inode to struct btrfs_inode

The structure is internal so we should use struct btrfs_inode for that.
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -4356,13 +4356,13 @@ void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
 		spin_lock(&block_group->lock);
 		if (test_and_clear_bit(BLOCK_GROUP_FLAG_IREF,
 				       &block_group->runtime_flags)) {
-			struct inode *inode = block_group->inode;
+			struct btrfs_inode *inode = block_group->inode;
 
 			block_group->inode = NULL;
 			spin_unlock(&block_group->lock);
 
 			ASSERT(block_group->io_ctl.inode == NULL);
-			iput(inode);
+			iput(&inode->vfs_inode);
 		} else {
 			spin_unlock(&block_group->lock);
 		}

fs/btrfs/block-group.h

@@ -115,7 +115,7 @@ struct btrfs_caching_control {
 
 struct btrfs_block_group {
 	struct btrfs_fs_info *fs_info;
-	struct inode *inode;
+	struct btrfs_inode *inode;
 	spinlock_t lock;
 	u64 start;
 	u64 length;

fs/btrfs/free-space-cache.c

@@ -137,7 +137,7 @@ struct inode *lookup_free_space_inode(struct btrfs_block_group *block_group,
 
 	spin_lock(&block_group->lock);
 	if (block_group->inode)
-		inode = igrab(block_group->inode);
+		inode = igrab(&block_group->inode->vfs_inode);
 	spin_unlock(&block_group->lock);
 	if (inode)
 		return inode;
@@ -156,7 +156,7 @@ struct inode *lookup_free_space_inode(struct btrfs_block_group *block_group,
 	}
 
 	if (!test_and_set_bit(BLOCK_GROUP_FLAG_IREF, &block_group->runtime_flags))
-		block_group->inode = igrab(inode);
+		block_group->inode = BTRFS_I(igrab(inode));
 	spin_unlock(&block_group->lock);
 
 	return inode;