Update FtdiSerialDriver.cs

Set the driver of the port correctly so that the permission request works. Otherwise, `Driver` would remain null. Verified in the debugger.

Author: ygoe

UsbSerialForAndroid/driver/FtdiSerialDriver.cs

@@ -59,7 +59,7 @@ public FtdiSerialDriver(UsbDevice device)
 
             for (int port = 0; port < device.InterfaceCount; port++)
             {
-                mPorts.Add(new FtdiSerialPort(mDevice, port));
+                mPorts.Add(new FtdiSerialPort(mDevice, port, this));
             }
         }
 
@@ -497,4 +497,4 @@ public static Dictionary<int, int[]> GetSupportedDevices()
             };
         }
     }
-}
+}