Simply advising startup companies doesn’t create a conflict. However, conflicts can arise if, for example: (a) you or the startup conduct commercial work in your lab, or (b) you are compensated by the startup and advise the startup more than the allowable number of days.
Here’s a good resource regarding conflicts of interests: https://researchcoi.berkeley.edu/faq.html
Note that UC Berkeley has a program administered by IPIRA that enables startups affiliated with the university’s accelerators to conduct new product R&D in faculty labs – under certain conditions. Learn about the Berkeley RIC Faculty Lab eXceptional-use for Innovation & Entrepreneurship (FLEXIE) program at https://ipira.berkeley.edu/entrepreneurs/berkeley-ric-flexie-program