serwb/scrambler: cleanup/fix potential bug

artiq/gateware/serwb/scrambler.py

@@ -98,16 +98,17 @@ class Descrambler(Module):
             NextState("SYNC_DATA")
         )
         fsm.act("SYNC_DATA",
-            If((sink.k[0] == 1) &
-               (sink.d[:8] == K(29,7)),
+            If(sink.stb,
+                If((sink.k == 1) & (sink.d == K(29,7)),
                     sink.ack.eq(1),
                     descrambler.reset.eq(1)
                 ).Else(
-                sink.ack.eq(source.ack),
-                source.stb.eq(sink.stb),
+                    source.stb.eq(1),
                     source.data.eq(descrambler.o),
-                If(source.stb & source.ack,
+                    If(source.ack,
+                        sink.ack.eq(1),
                         descrambler.ce.eq(1)
                     )
                 )
             )
+        )