Fix compiler warning: comparison between signed...

... and unsigned integer expressions [-Wsign-compare]

DHT.cpp

@@ -26,7 +26,7 @@
 #include "DHT.h"
 
 #define MIN_INTERVAL 2000 /**< min interval value */
-#define TIMEOUT -1        /**< timeout on */
+#define TIMEOUT UINT32_MAX /**< Used programmatically for timeout. Not a timeout duration. Type: uint32_t. */
 
 /*!
  *  @brief  Instantiates a new DHT class