driver/usbvideodriver: use playbin3 element

Decoding via VA-API fails for the C920 model and the playbin element on
AMD graphic cards, playbin3 has no problems though - so lets switch to
that.

Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>

labgrid/driver/usbvideodriver.py

@@ -131,7 +131,7 @@ def stream(self, caps_hint=None, controls=None):
         tx_cmd = self.video.command_prefix + ["gst-launch-1.0", "-q"]
         tx_cmd += pipeline.split()
         rx_cmd = ["gst-launch-1.0"]
-        rx_cmd += "playbin uri=fd://0".split()
+        rx_cmd += "playbin3 uri=fd://0".split()
 
         tx = subprocess.Popen(
             tx_cmd,