btrfs: qgroup: remove redundant check for add_qgroup_rb() call

The add_qgroup_rb() function never returns an error pointer anymore since
commit 8d54518 ("btrfs: qgroup: pre-allocate btrfs_qgroup to reduce
GFP_ATOMIC usage"), so checking for an error pointer result at
btrfs_quota_enable() is redundant.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/qgroup.c

@@ -1161,11 +1161,6 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
 
 			qgroup = add_qgroup_rb(fs_info, prealloc, found_key.offset);
 			prealloc = NULL;
-			if (IS_ERR(qgroup)) {
-				ret = PTR_ERR(qgroup);
-				btrfs_abort_transaction(trans, ret);
-				goto out_free_path;
-			}
 			ret = btrfs_sysfs_add_one_qgroup(fs_info, qgroup);
 			if (ret < 0) {
 				btrfs_abort_transaction(trans, ret);