kselftest: Fix error message for unconfigured LLVM builds

We are missing a ) when we attempt to complain about not having enough
configuration for clang, resulting in the rather inscrutable error:

../lib.mk:23: *** unterminated call to function 'error': missing ')'.  Stop.

Add the required ) so we print the message we were trying to print.
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/lib.mk

@@ -20,7 +20,7 @@ CLANG_TARGET_FLAGS              := $(CLANG_TARGET_FLAGS_$(ARCH))
 
 ifeq ($(CROSS_COMPILE),)
 ifeq ($(CLANG_TARGET_FLAGS),)
-$(error Specify CROSS_COMPILE or add '--target=' option to lib.mk
+$(error Specify CROSS_COMPILE or add '--target=' option to lib.mk)
 else
 CLANG_FLAGS     += --target=$(CLANG_TARGET_FLAGS)
 endif # CLANG_TARGET_FLAGS