selftests: timers: clocksource-switch: fix passing errors from child

The return value from system() is a waitpid-style integer. Do not return
it directly because with the implicit masking in exit() it will always
return 0. Access it with appropriate macros to really pass on errors.

Fixes: 7290ce14 ("selftests/timers: Add clocksource-switch test from timetest suite")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: John Stultz <jstultz@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/timers/clocksource-switch.c

@@ -110,10 +110,10 @@ int run_tests(int secs)
 
 	sprintf(buf, "./inconsistency-check -t %i", secs);
 	ret = system(buf);
-	if (ret)
-		return ret;
+	if (WIFEXITED(ret) && WEXITSTATUS(ret))
+		return WEXITSTATUS(ret);
 	ret = system("./nanosleep");
-	return ret;
+	return WIFEXITED(ret) ? WEXITSTATUS(ret) : 0;
 }