kukui: Fix adc read crashes EC.
kukui: Fix adc read crashes EC.

The ADC module is diabled after reading the BOARD_ID on system booted.
This will hang the adc reading once we commanding "adc" to EC after
that, and thus triggers wathdog.

TEST=BOOTBLOCK=... make BOARD=kukui -j flash_ec.
     See AP booted; type "adc" in EC console, and see that it won't
     trigger watchdog.
BRANCH=None
BUG=b:122995670

Change-Id: Id13d6ceddf74a06b741ab0c834c75409ab580c74
Signed-off-by: Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1416074
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@chromium.org>
Reviewed-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec