mfg_servo_v4: Fixup atmega programming logic.

Previous implementation relied 7 of the 8bits of ioexpander
port 0 output register remaining constant, which is no longer the case
when I tested.

This CL, instead uses a mask (0x2) to compare only the atmega_rst bit
in the output register instead.

BUG=chromium:931904
TEST=manual,

serial="C1700000000"
mac="00:00:00:00:00:00"
sudo emerge dfu-programmer
sudo ./mfg_servo_v4.py -s $serial -m $mac --no_flash

See atmega programmed successfully
Try both atmega_rst asserted and de-asserted before executing.

Change-Id: I209d4faabb486c23c1709ff91eb4a55b6ef98cb9
Reviewed-on: https://chromium-review.googlesource.com/1575827
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
1 file changed