ast: duplicated code gen for embedded generic fields

[shove70]

This PR fixed: duplicated code gen for embedded generic fields

struct Foo[T] {
	field T
}

struct MainStruct[T] {
	Foo[T]
}

fn main() {
	m := MainStruct[int]{}
	println(m.field)
}

code gen:

now:

VV_LOCAL_SYMBOL void main__main(void) {
	main__MainStruct_T_int m = ((main__MainStruct_T_int){.Foo = ((main__Foo_T_int){.field = 0,}),});
	println(int_str(m.Foo.field));
}