avoid unused-variable warning

Avoid warning when compiled with All warnings enabled. 
.../src/NimBLEScan.cpp: In member function 'void NimBLEScanResults::dump() const':
.../src/NimBLEScan.cpp:481:22: warning: unused variable 'dev' [-Wunused-variable]
  481 |     for (const auto& dev : m_deviceVec) {
      |                      ^~~

Author: mazgch

src/NimBLEScan.cpp

@@ -480,7 +480,10 @@ void NimBLEScan::clearResults() {
 void NimBLEScanResults::dump() const {
     for (const auto& dev : m_deviceVec) {
         NIMBLE_LOGI(LOG_TAG, "- %s", dev->toString().c_str());
-    }
+#if CONFIG_NIMBLE_CPP_LOG_LEVEL < 3
+        (void)dev;
+#endif
+     }
 } // dump
 
 /**