Update usb_desc.h

fixes #524

teensy3/usb_desc.h

@@ -734,7 +734,7 @@ let me know?  http://forum.pjrc.com/forums/4-Suggestions-amp-Bug-Reports
   #define ENDPOINT1_CONFIG	ENDPOINT_TRANSMIT_ONLY
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_ONLY
   #define ENDPOINT3_CONFIG	ENDPOINT_TRANSMIT_AND_RECEIVE
-  #define ENDPOINT4_CONFIG	ENDPOINT_TRANSMIT_ONLY
+  #define ENDPOINT4_CONFIG	ENDPOINT_TRANSMIT_AND_RECEIVE
 
 #elif defined(USB_AUDIO)
   #define VENDOR_ID		0x16C0