You need to specify the right serial port and baud rate that the Pixhawk is connected to with the --master option. If you are using usb, the pixhawk will appear as /dev/ttyACM0 or /dev/ttyACM1 (you can do ls /dev/tty* to see which ports you have). If you are using the UART on the raspberry pi, like in your pictures, you should connect to /dev/ttyAMA0 if you are using a raspberry pi 2 or /dev/ttyS0 if you are using a raspberry pi3. If you want to use the UART, you will also have to disable the console. The baudrate is controlled by the SERIAL parameters on the pixhawk Complete Parameter List — Copter documentation.
-Jacob