btrfs: remove cached space_info in btrfs_statfs()

In btrfs_statfs() we cache fs_info::space_info in a local variable only
to use it once in a list_for_each_rcu() statement.

Not only is the local variable unnecessary it even makes the code harder
to follow as it's not clear which list it is iterating.
Signed-off-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -2021,7 +2021,6 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(dentry->d_sb);
 	struct btrfs_super_block *disk_super = fs_info->super_copy;
-	struct list_head *head = &fs_info->space_info;
 	struct btrfs_space_info *found;
 	u64 total_used = 0;
 	u64 total_free_data = 0;
@@ -2035,7 +2034,7 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	int mixed = 0;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(found, head, list) {
+	list_for_each_entry_rcu(found, &fs_info->space_info, list) {
 		if (found->flags & BTRFS_BLOCK_GROUP_DATA) {
 			int i;