DebugInfo: Use DILexicalBlockFile::getContext() over getScope()
DebugInfo: Use DILexicalBlockFile::getContext() over getScope()

`getScope()` passes the scope back through a `DILexicalBlock` even
though the underlying pointer may be an incompatible `MDSubprogram`.
Just use `getContext()` directly.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@234245 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang