Add missing microsecondsToClockCycles for 33 BLE

Author: tjpetz

DHT.h

@@ -47,6 +47,13 @@
 #define DHT21 21  /**< DHT TYPE 21 */
 #define AM2301 21 /**< AM2301 */
 
+#if (TARGET_NAME==ARDUINO_NANO33BLE)
+// As of 7 Sep 2020 the Arduino Nano 33 BLE boards do not have microsecondsToClockCycles defined.
+#ifndef microsecondsToClockCycles
+#define microsecondsToClockCycles(a) ( (a) * (SystemCoreClock / 1000000L) )
+#endif
+#endif
+
 /*!
  *  @brief  Class that stores state and functions for DHT
  */