[lldb][NFC] Use static_cast instead of reinterpret_cast where possible

Summary: There are a few places in LLDB where we do a `reinterpret_cast` for conversions that we could also do with `static_cast`. This patch moves all this code to `static_cast`.

Reviewers: shafik, JDevlieghere, labath

Reviewed By: labath

Subscribers: arphaman, usaxena95, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D72161