faft: Fix servo.enter_key() in firmware_FAFTSetup

A typo in a previous change. Should be servo.enter_key() instead of
servo.enter().

BUG=chrome-os-partner:39653
TEST=None

Change-Id: I354d9f0d4073abfa70f58126011488f4f88f5117
Reviewed-on: https://chromium-review.googlesource.com/270265
Trybot-Ready: Tom Tam <waihong@google.com>
Tested-by: Tom Tam <waihong@google.com>
Reviewed-by: danny chan <dchan@chromium.org>
Commit-Queue: Tom Tam <waihong@google.com>
1 file changed