the BIOS file seem to be automatically added by the install script anyway - you don't have to do anything: https://github.com/RetroPie/RetroPie-Setup/blob/master/scriptmodules/libretrocores/lr-ppsspp.sh#L61
@nibio74, whoever that is, made the change here. I'll revert it, having no means to contact them :/
https://github.com/RetroPie/RetroPie-Setup/wiki/PSP/_compare/b62096615b65075de1355213c380d30cf767fb61...5d7b9b5c9e234664da5b43c706f917a7855ec99c