change parameter to signed int

As of wrong paramater, the following problem existed, that will be fixed now with this change.

BTScanResultsSet.cpp:67:8: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
if (i < 0)

Author: iltis42

libraries/BluetoothSerial/src/BTScan.h

@@ -24,19 +24,19 @@ class BTScanResults {
 
     virtual void        		dump(Print *print = nullptr);
     virtual int         		getCount();
-    virtual BTAdvertisedDevice* getDevice(uint32_t i);
+    virtual BTAdvertisedDevice* getDevice(int i);
 };
 
 class BTScanResultsSet : public BTScanResults {
 public:
     void                	dump(Print *print = nullptr);
     int                 	getCount();
-    BTAdvertisedDevice*		getDevice(uint32_t i);
+    BTAdvertisedDevice*		getDevice(int i);
 
 	bool add(BTAdvertisedDeviceSet advertisedDevice, bool unique = true);
 	void clear();
 
     std::map<std::string, BTAdvertisedDeviceSet> m_vectorAdvertisedDevices;
 };
 
-#endif
+#endif