freertos: Fix unused variable warning

This commit fixes an unused variable warning when
configASSERT is undefined.

components/freertos/queue.c

@@ -338,6 +338,7 @@ Queue_t * const pxQueue = ( Queue_t * ) xQueue;
 			the real queue and semaphore structures. */
 			volatile size_t xSize = sizeof( StaticQueue_t );
 			configASSERT( xSize == sizeof( Queue_t ) );
+			( void ) xSize; /* Keeps lint quiet when configASSERT() is not defined. */
 		}
 		#endif /* configASSERT_DEFINED */