[clang] [analyzer] Only report the first dereference of the same variable in DanglingPtrDeref (PR #215409)

[Benedek Kaibas via cfe-commits]

benedekaibas wrote:

In [71cc370](https://github.com/llvm/llvm-project/pull/215409/commits/71cc3708e2858247327d0095384a7e503d427de7) I have updated the doc comment to reflect the correct behavior of the function. The earlier comment present in [c2cd1ff](https://github.com/llvm/llvm-project/pull/215409/commits/c2cd1ff1c6cee173fd9381a353b288fc77481aaa) was for the earlier stage of the function during development. 

https://github.com/llvm/llvm-project/pull/215409