ci: clang: Use LLVM_TOOLCHAIN_PATH instead of CLANG_ROOT_DIR
ci: clang: Use LLVM_TOOLCHAIN_PATH instead of CLANG_ROOT_DIR

`CLANG_ROOT_DIR` is deprecated; use `LLVM_TOOLCHAIN_PATH` instead.

Signed-off-by: Stephanos Ioannidis <dc76e9f0c0006e8f919e0c515c66dbba3982f785@stephanos.io>

finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr