[clang] Fix error that reference to PointerType is ambiguous in clang/lib/Analysis/UnsafeBufferUsage.cpp (PR #142966)

[Abhina Sree via cfe-commits]

abhina-sree wrote:

> LGTM, but I would also consider dropping the "using namespace llvm" instead. This seems a bit unusual for a file in clang/lib/Analysis.

Thanks! I've implemented your suggested solution instead

https://github.com/llvm/llvm-project/pull/142966