tb: axis_replay_buffer: Don't delay on last-sent byte

We don't need to delay after sending the last byte, and it makes it more
difficult to time subsequent packets correctly.

Signed-off-by: Sean Anderson <seanga2@gmail.com>

tb/axis_replay_buffer.py

@@ -29,7 +29,7 @@ async def send_packet(signals, packet, ratio=1):
             if signals['ready'].value:
                 break
         signals['valid'].value = 0
-        if ratio != 1:
+        if ratio != 1 and not last:
             await ClockCycles(signals['clk'], ratio - 1, rising=False)
 
 @timeout(30, 'us')