minidiag/ui: Prevent calling update action if there were no updates

Add a return code `VB2_ERROR_EX_DIAG_TEST_UPDATED` to determine if
updating needed.

BUG=b:168776970
BRANCH=none
TEST=Build locally, boot recovery, select 'run diagnostics',
     enter memory test (quick) screen,
     and observe that the delay reduces while pressing keyboard

Cq-Depend: chromium:2423699
Signed-off-by: Hsuan Ting Chen <roccochen@chromium.org>
Change-Id: I7606911bee7257e8eed4ec35d197efaa57b72e13
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2424370
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
3 files changed