debug_link: Fix error message for DebugLinkMissingError

When raising DebugLinkMissingError, the error message should use
_VENDOR_ID and _PRODUCT_ID values instead of their key names.

BUG=None
TEST=Manual tests and unittests

Change-Id: I98c69460b1f12ff8e79fc8ed27a9cc6690ab72ac
Reviewed-on: https://chromium-review.googlesource.com/262221
Tested-by: Yiming Chen <yimingc@chromium.org>
Reviewed-by: David Pursell <dpursell@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Yiming Chen <yimingc@chromium.org>
1 file changed