Fix initialization with CH340 UARTs

Initialization is messed up on older Linux kernels and that results
in 9600 baud being used unconditionally in some cases. Setting the
baud rate separately seems to work around this successfully.

Fixes grigorig/stcgal#5.

stcgal/protocols.py

@@ -732,8 +732,10 @@ class StcBaseProtocol:
         Set up serial port, send sync sequence and get part info.
         """
 
-        self.ser = serial.Serial(port=self.port, baudrate=self.baud_handshake,
-                                 parity=self.PARITY)
+        self.ser = serial.Serial(port=self.port, parity=self.PARITY)
+        # set baudrate separately to work around a bug with the CH340 driver
+        # on older Linux kernels
+        self.ser.baudrate = self.baud_handshake
 
         # fast timeout values to deal with detection errors
         self.ser.timeout = 0.5