Use os drivers de aqui e siga as instruções.
1:
apt-get install linux-image-$(uname -r|sed 's,[^-]*-[^-]*-,,') linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,') broadcom-sta-dkms
2:
modprobe -r b44 b43 b43legacy ssb brcmsmac bcma
3:
modprobe wl