firmware_builder: always create metrics file
firmware_builder: always create metrics file

The firmware builder doesn't need to do anything for code coverage,
except that it still needs to create a metrics file so that the
postsubmit builder can find it.

BUG=chromium:1182320
BRANCH=None
TEST=firmware-ec-cov-cq succeeds

Cq-Include-Tryjobs: chromeos/cq:firmware-ec-cov-cq

Signed-off-by: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@google.com>
Change-Id: Id1a4ac5cee1ba4bfbfb2f68ce937386658abfa4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2722554
Commit-Queue: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@chromium.org>
Tested-by: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@chromium.org>
Reviewed-by: LaMont Jones <01939f9990a33aa2509cfaed21d2f9ba201a2b37@chromium.org>
Reviewed-by: Sean McAllister <ed4d2242d1138bb5c12488824add2e57e1144bd4@google.com>

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