[Driver][NFC] Update Cases usage and unused variable (#21336)
Update usage of Cases statements to use lists. This cleans up the build
warning being emitted.
warning: ‘llvm::StringSwitch<T, R>& llvm::StringSwitch<T,
R>::Cases(llvm::StringLiteral, llvm::StringLiteral, T) [with T =
llvm::StringRef; R = llvm::StringRef]’ is deprecated: Pass cases in
std::initializer_list instead [-Wdeprecated-declarations]
1089 | llvm::StringSwitch<StringRef>(DeviceName)
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1090 | .Cases("intel_gpu_bdw", "intel_gpu_8_0_0", "bdw")
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Also clean up an unused variable in Driver.cpp
