There's a merged pull request on the void-packages repository

broadcom-wl-dkms: add linux-5.9.patch
https://github.com/void-linux/void-packages/pull/27202

Description:
Linux 5.9 broke broadcom-wl-dkms.  Add patch[0] from archlinux package
to fix.

[0] https://raw.githubusercontent.com/archlinux/svntogit-community/packages/broadcom-wl-dkms/trunk/011-linux59.patch