Fix a compiler warning.

FossilOrigin-Name: 6df99e52dabf2a243ad635529649b86c21735e91

src/sqliteInt.h

@@ -1235,7 +1235,7 @@ struct VTable {
   sqlite3_vtab *pVtab;      /* Pointer to vtab instance */
   int nRef;                 /* Number of pointers to this structure */
   u8 bConstraint;           /* True if constraints are supported */
-  u32 iSavepoint;           /* Depth of the SAVEPOINT stack */
+  int iSavepoint;           /* Depth of the SAVEPOINT stack */
   VTable *pNext;            /* Next in linked list (see above) */
 };