SEGFAULT in get_column_grant()

Due to a typo, the wrong grant_table was used when fetching privileges
for roles.
Signed-off-by: Vicențiu Ciorbaru <vicentiu@mariadb.org>

sql/sql_acl.cc

@@ -7453,7 +7453,8 @@ ulong get_column_grant(THD *thd, GRANT_INFO *grant,
       if (!grant_column)
         priv|= (grant->privilege | grant_table_role->privs);
       else
-        priv|= (grant->privilege | grant_table->privs | grant_column->rights);
+        priv|= (grant->privilege | grant_table_role->privs |
+                grant_column->rights);
     }
   }
   mysql_rwlock_unlock(&LOCK_grant);