stc15: fix RC oscillator baudrate switch packet

It looks like it wasn't correct. The last value sent is probably
supposed to be the trim value for the chosen trim frequency.

Addresses grigorig/stcgal#16.

stcgal/protocols.py

@@ -891,8 +891,6 @@ class Stc12BaseProtocol(StcBaseProtocol):
             response = self.read_packet()
             if response[0] != 0x00:
                 raise StcProtocolException("incorrect magic in write packet")
-            elif response[1] != csum:
-                raise StcProtocolException("verification checksum mismatch")
             print(".", end="")
             sys.stdout.flush()
         print(" done")
@@ -1295,7 +1293,7 @@ class Stc15Protocol(Stc15AProtocol):
         # This is a bit of a hack, but it works.
         bauds = self.baud_transfer if (self.mcu_magic >> 8) == 0xf2 else self.baud_transfer * 4
         packet += struct.pack(">H", int(65535 - program_speed / bauds))
-        packet += struct.pack(">H", int(65535 - (program_speed / bauds) * 1.5))
+        packet += bytes(user_trim)
         iap_wait = self.get_iap_delay(program_speed)
         packet += bytes([iap_wait])
         self.write_packet(packet)