To be found guilty under Section 9 of the Prevention of Bribery Ordinance (防止賄賂條例), the agent (you in this case) must solicits or accepts any advantage (索取或接受任何利益). There will be no case if no advantage has been involved.
However - even this is not illegal, you can still by terminated for cause due to conflict of interest.
It will be best if you don't involve in the process at all and disclose the conflict of interest. (Beside - if the company is driven by cost, B company will get the contract regardless of your involvement.)