Pass nameTag to nested structs

```go
type A struct {
	A string `json:"a" validate:"long"`
}

type B struct{
	A
	B string `json:"b" validate:"long"`
}

b := B{...}
errs := V.ValidateAndTag(b, "json")

// Without this fix
errs[0].Field == "A"

// With this fix
errs[0].Field == "a"
```