Add const qualifiers to Host mode Class drivers.

Fix KeyboardHost ClassDriver demo; boot protocol keyboard report structure in the Host Mode HID Class driver uses the full keycode array from the attached device.

LUFA/Drivers/USB/LowLevel/Pipe.c

@@ -70,7 +70,7 @@ void Pipe_ClearPipes(void)
 	}
 }
 
-bool Pipe_IsEndpointBound(uint8_t EndpointAddress)
+bool Pipe_IsEndpointBound(const uint8_t EndpointAddress)
 {
 	uint8_t PrevPipeNumber = Pipe_GetCurrentPipe();
 

LUFA/Drivers/USB/LowLevel/Pipe.h

@@ -809,7 +809,7 @@
 			 *
 			 *  \return Boolean true if a pipe bound to the given endpoint address is found, false otherwise
 			 */
-			bool Pipe_IsEndpointBound(uint8_t EndpointAddress);
+			bool Pipe_IsEndpointBound(const uint8_t EndpointAddress);
 		
 			/** Reads and discards the given number of bytes from the pipe, discarding fully read packets from the host
 			 *  as needed. The last packet is not automatically discarded once the remaining bytes has been read; the