btrfs: qgroup: cleanup the unused srcroot from btrfs_qgroup_inherit

Since commit 0b246afa ("btrfs: root->fs_info cleanup, add fs_info
convenience variables"), the srcroot is no longer used to get
fs_info::nodesize.  In fact, it can be dropped after commit 707e8a07
("btrfs: use nodesize everywhere, kill leafsize").
Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/qgroup.c

@@ -2287,22 +2287,6 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans,
 	if (ret)
 		goto out;
 
-	if (srcid) {
-		struct btrfs_root *srcroot;
-		struct btrfs_key srckey;
-
-		srckey.objectid = srcid;
-		srckey.type = BTRFS_ROOT_ITEM_KEY;
-		srckey.offset = (u64)-1;
-		srcroot = btrfs_read_fs_root_no_name(fs_info, &srckey);
-		if (IS_ERR(srcroot)) {
-			ret = PTR_ERR(srcroot);
-			goto out;
-		}
-
-		level_size = fs_info->nodesize;
-	}
-
 	/*
 	 * add qgroup to all inherited groups
 	 */
@@ -2359,6 +2343,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans,
 		 * our counts don't go crazy, so at this point the only
 		 * difference between the two roots should be the root node.
 		 */
+		level_size = fs_info->nodesize;
 		dstgroup->rfer = srcgroup->rfer;
 		dstgroup->rfer_cmpr = srcgroup->rfer_cmpr;
 		dstgroup->excl = level_size;