update_release_branch: fix the cros lint error
update_release_branch: fix the cros lint error

When using the repo upload, the cros lint output the error below.
This patch fixes the error below.

Hook script "cros lint ${PRESUBMIT_FILES}" failed with code 1:
  ERROR: /mnt/host/source/src/platform/ec/util/update_release_branch.py \
Imports are incorrectly sorted and/or formatted.

BUG=None
BRANCH=None
TEST=repo upload

Signed-off-by: Zhuohao Lee <916bf7ddbf0565669e59e3cb2b613381a48066c0@chromium.org>
Change-Id: I78b617c10956081f24f81de5c7ad9e65547557e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3650296
Reviewed-by: caveh jalali <08e24a66aefda7a55ca7d73f8903e0fb16eec763@chromium.org>
Reviewed-by: Boris Mittelberg <46897f4fb5cad4b1d5146ad1fd460d7f4825bbf7@google.com>

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