Analyze mem metrics display a negative number

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1. create table and insert some data
2. analyze data
3. check metrics

### 2. What did you expect to see? (Required)
memory of analyze metrics correct
### 3. What did you see instead (Required)

### 4. What is your TiDB version? (Required)
```sql
TiDB root@127.0.0.1:rtdb> select tidb_version();
+-----------------------------------------------------------+
| tidb_version() |
+-----------------------------------------------------------+
| Release Version: v6.7.0-alpha |
| Edition: Community |
| Git Commit Hash: ed1b4cf44890e4346849bce7c9297bde7e7abee5 |
| Git Branch: heads/refs/tags/v6.7.0-alpha |
| UTC Build Time: 2023-03-13 14:34:57 |
| GoVersion: go1.20.2 |
| Race Enabled: false |
| TiKV Min Version: 6.2.0-alpha |
| Check Table Before Drop: false |
| Store: tikv |
+-----------------------------------------------------------+
1 row in set
```