[clang][Interp][NFC] Fix some build warnings

Fixes:
/buildbot/worker/arc-folder/llvm-project/clang/lib/AST/Interp/Disasm.cpp:143:25: warning: cast from type 'const clang::interp::Block*' to type 'void*' casts away qualifiers [-Wcast-qual]
/buildbot/worker/arc-folder/llvm-project/clang/lib/AST/Interp/Disasm.cpp:271:23: warning: cast from type 'const clang::interp::Block*' to type 'void*' casts away qualifiers [-Wcast-qual]