[HLSL] Erroneous register validation warning on structs with resources in base class

Register type validation does not seem to be scanning base classes when looking for resources in a structure/class. The following code is valid and in Clang it produces two warnings.

```
struct A {
RWBuffer BufA;
StructuredBuffer BufB;
};

struct B : A {
};

B b : register(u10) : register(t20);

[numthreads(4,1,1)]
void main() {
}
```

Warnings reported:
```
:9:3: warning: binding type 'u' only applies to types containing UAV resources [-Wlegacy-constant-register-binding]
9 | B b : register(u10) : register(t20);
| ^
:9:3: warning: binding type 't' only applies to types containing SRV resources [-Wlegacy-constant-register-binding]
2 warnings generated.
```
https://godbolt.org/z/qvKKPPr8d