selftests: vDSO: vdso_test_getrandom: Avoid -Wunused

vgetrandom_put_state() and the variable "ret" in kselftest() are unused.

Drop the variable "ret". Suppress the warning for  vgetrandom_put_state()
as it is meant as an example for libc implementors.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250611-selftests-vdso-fixes-v3-4-e62e37a6bcf5@linutronix.de

tools/testing/selftests/vDSO/vdso_test_getrandom.c

@@ -100,6 +100,7 @@ out:
 	return state;
 }
 
+__attribute__((unused)) /* Example for libc implementors */
 static void vgetrandom_put_state(void *state)
 {
 	if (!state)
@@ -264,7 +265,7 @@ static void kselftest(void)
 	}
 	for (;;) {
 		struct ptrace_syscall_info info = { 0 };
-		int status, ret;
+		int status;
 		ksft_assert(waitpid(child, &status, 0) >= 0);
 		if (WIFEXITED(status)) {
 			ksft_assert(WEXITSTATUS(status) == 0);