Fix compiler warning: no-return-in-nonvoid-function simtrace2_usb.c

RPM post-build-checks found some issue and marks these as error:
[   61s] I: Program returns random data in a function
[   61s] E: simtrace2 no-return-in-nonvoid-function simtrace2_usb.c:88

Change-Id: Id16fb7fc4f13176b2b6443af02a5848d8fcfb069

host/simtrace2_usb.c

@@ -85,4 +85,5 @@ int main(int argc, char **argv)
 {
 	libusb_init(NULL);
 	find_devices();
+	return 0;
 }