[Attributor][Fix] Manifest nocapture only in CSArgument or Argument

Summary:
We can query to Attributor whether the value is captured in the scope or not on the following way:

```
    const auto & NoCapAA = A.getAAFor<AANoCapture>(*this, IRPosition::value(V));
```
And if V is CallSiteReturned then `getDeducedAttribute` will add `nocatpure` to the callsite returned value. It is not valid.
This patch checks the position is an argument or call site argument.

This is tested in D67286.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67342

llvm-svn: 371589