Fix LoadKernel() failing to update GPT flags.

BUG=5654

TEST=manual

Case 1: Trying a new kernel which works
  sudo cgpt add -P10 -T10 -S0 -i4 /dev/sda
Then reboot and
  sudo cgpt show /dev/sda
See that tries is now 9 for /dev/sda4 (since the current ChromeOS
doesn't set the successful bit)

Case 2: Trying a new kernel which is bad
  sudo dd if=/dev/zero of=/dev/sda4 count=1 conv=notrunc
Then reboot and
  sudo cgpt show /dev/sda4
See that success=prio=tries=0 for /dev/sda4.

Review URL: http://codereview.chromium.org/3130040
2 files changed