Correctly propagate error

The `pkg/parser/ast/dml.go` file has some functions where the returned error is not checked and the error is not bubbled up when calling "Restore()" method

There are 3 calls to `` where this happens:

https://github.com/pingcap/tidb/blob/master/pkg/parser/ast/dml.go#L3456
https://github.com/pingcap/tidb/blob/master/pkg/parser/ast/dml.go#L3463
https://github.com/pingcap/tidb/blob/master/pkg/parser/ast/dml.go#L3525

This was discovered when implementing custom types (Not using `parser_driver` or `test_driver`) and the Restore method implementation of either the ValueExpr or the ParamMarkerExpr was returning an error.
I this case, Restore was still returning `nil` and the generated string from Restore call was an invalid SQL query.