Use osmo_libusb_{init,exit}() instead of libusb_{init,exit}()

We use other osmo_libusb_* functions later in the code, so it is best
to initialize the library via libosmousb, and not directly.

Change-Id: I2fd981935e1420e529f5dd8a98edd347c317284c

host/src/simtrace2_usb.c

@@ -77,7 +77,7 @@ static int find_devices(void)
 
 int main(int argc, char **argv)
 {
-	libusb_init(NULL);
+	osmo_libusb_init(NULL);
 	find_devices();
 	return 0;
 }