tb: descramble: Expand offset search

If we get very lucky, the descrambler can lock after only 28 bits
(the size of the idle counter). Take this scenario into account when
deciding on the offset.

Fixes: 12a4678 ("Add (de)scrambling support")
Signed-off-by: Sean Anderson <seanga2@gmail.com>

tb/descramble.py

@@ -80,7 +80,7 @@ async def test_descramble(descrambler, valids):
 
     best_corr = -1
     best_off = None
-    for off in range(30, 42):
+    for off in range(28, 42):
         corr = sum(i == o for i, o in zip(ins[off:], outs))
         if corr > best_corr:
             best_corr = corr