selftests: watchdog: prefer strtoul() over atoi()

commit f15d7114 ("Documentation/watchdog: add timeout and ping rate
control to watchdog-test.c") used both atoi() and strtoul() for string
to integer conversion. As usage of atoi() is discouraged in newer code,
replace it with strtoul() for consistency.
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/watchdog/watchdog-test.c

@@ -106,7 +106,7 @@ int main(int argc, char *argv[])
 			printf("Watchdog ping rate set to %u seconds.\n", ping_rate);
 			break;
 		case 't':
-			flags = atoi(optarg);
+			flags = strtoul(optarg, NULL, 0);
 			ret = ioctl(fd, WDIOC_SETTIMEOUT, &flags);
 			if (!ret)
 				printf("Watchdog timeout set to %u seconds.\n", flags);