Revert "Remove SUID bit for nvidia-modprobe"

I apologize, but it seems that although this worked fine on my rig, it is causing issues with creating /dev nodes, in particular /dev/nvidiactl, causing issues like #20 (closed) and #19 (closed). Man nvidia-modprobe says:

Users should not normally need to run nvidia-modprobe by hand: the NVIDIA user-space driver components will fork(2)/exec(3) it when needed.

This seems to be the reason why the SUID is still needed. I'm thinking about the possibility of replacing this with additional calls to nvidia-modprobe to create all /dev nodes in our udev rules, let me know if that solution would also suit.

Fixes: #19 (closed) #20 (closed)