[CUDA] Fix "control reaches end of non-void function" warnings in Cuda.cpp.
[CUDA] Fix "control reaches end of non-void function" warnings in Cuda.cpp.

Some compilers are too dumb to realize that the switch statement covers
all cases.

(Don't use a "default" label, because we explicitly want to get a warning
if our switch doesn't cover all the cases.)

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@274713 91177308-0d34-0410-b5e6-96231b3b80d8

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