btrfs: unify extent buffer allocation api

Make the extent buffer allocation interface consistent.  Cloned eb will
set a valid fs_info.  For dummy eb, we can drop the length parameter and
set it from fs_info.

The built-in sanity checks may pass a NULL fs_info that's queried for
nodesize, but we know it's 4096.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/tests/qgroup-tests.c b/fs/btrfs/tests/qgroup-tests.c
index ec3dcb2..7336b1c 100644
--- a/fs/btrfs/tests/qgroup-tests.c
+++ b/fs/btrfs/tests/qgroup-tests.c
@@ -404,6 +404,16 @@
 		ret = -ENOMEM;
 		goto out;
 	}
+	/* We are using this root as our extent root */
+	root->fs_info->extent_root = root;
+
+	/*
+	 * Some of the paths we test assume we have a filled out fs_info, so we
+	 * just need to add the root in there so we don't panic.
+	 */
+	root->fs_info->tree_root = root;
+	root->fs_info->quota_root = root;
+	root->fs_info->quota_enabled = 1;
 
 	/*
 	 * Can't use bytenr 0, some things freak out
@@ -448,17 +458,6 @@
 		goto out;
 	}
 
-	/* We are using this root as our extent root */
-	root->fs_info->extent_root = root;
-
-	/*
-	 * Some of the paths we test assume we have a filled out fs_info, so we
-	 * just need to addt he root in there so we don't panic.
-	 */
-	root->fs_info->tree_root = root;
-	root->fs_info->quota_root = root;
-	root->fs_info->quota_enabled = 1;
-
 	test_msg("Running qgroup tests\n");
 	ret = test_no_shared_qgroup(root);
 	if (ret)