Little bit of codec_init clean up

In Main File
- added extra code to handle first half of a stop bit (125-6)
- took out the +1s in the ack handling code- probably more confusing
than descriptive (130)
- Used clearer method for shifting the register (line 135)
In Testbench
- uses the shorter form of the port map (line 21)
- uses the better 'toggle type' of clock (line 38 and surrounding lines)