drivers/xbee: add UL to constants for 8 and 16 bit compatibility

drivers/xbee/xbee.c

@@ -41,11 +41,11 @@
 /**
  * @brief   Delay when entering command mode, must be > 1s
  */
-#define ENTER_CMD_MODE_DELAY        (1100U * 1000U)
+#define ENTER_CMD_MODE_DELAY        (1100UL * US_PER_MS)
 /**
  * @brief   Delay when resetting the device, 10ms
  */
-#define RESET_DELAY                 (10U * 1000U)
+#define RESET_DELAY                 (10UL * US_PER_MS)
 
 /**
  * @brief   Timeout for receiving AT command response