reset the db privilege cache when revoking db priviges on DROP ROLE

mysql-test/suite/roles/set_and_drop.result

@@ -95,6 +95,8 @@ pr1
 pr1
 drop role role1;
 flush tables;
+select * from mysql.roles_mapping;
+ERROR 42000: SELECT command denied to user 'foo'@'localhost' for table 'roles_mapping'
 select * from mysqltest1.t1;
 ERROR 42000: SELECT command denied to user 'foo'@'localhost' for table 't1'
 select a from mysqltest1.t2;

sql/sql_acl.cc

@@ -8882,6 +8882,7 @@ static int handle_grant_data(TABLE_LIST *tables, bool drop,
       /* If search is requested, we do not need to search further. */
       if (search_only)
         goto end;
+      acl_cache->clear(1);
     }
   }