cros_update_firmware: clean edb cache before emerge firmware for the board

BUG=b:122467913
TEST=run cros_update_firmware for flapjack board after modifying its firmware config

Change-Id: I9ef0bbafe3abb6ac5555f9382e9dc381256b24e1
Reviewed-on: https://chromium-review.googlesource.com/1448960
Commit-Ready: Ned Nguyen <[email protected]>
Tested-by: Ned Nguyen <[email protected]>
Reviewed-by: Ned Nguyen <[email protected]>
(cherry picked from commit fc67e1f1e5ff6d9af17d726665e210a33e2baac9)
Reviewed-on: https://chromium-review.googlesource.com/c/1480750
Commit-Queue: Chris Zhou <[email protected]>
Tested-by: Chris Zhou <[email protected]>
Reviewed-by: YH Lin <[email protected]>
1 file changed