nixos/nvidia: make nvidia-frontend device major constant

It is assigned by https://www.kernel.org/doc/Documentation/admin-guide/devices.txt
and never changes, so we can skip grep.

nixos/modules/hardware/video/nvidia.nix

@@ -361,10 +361,10 @@ in
     services.udev.extraRules =
       ''
         # Create /dev/nvidia-uvm when the nvidia-uvm module is loaded.
-        KERNEL=="nvidia", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidiactl c $$(grep nvidia-frontend /proc/devices | cut -d \  -f 1) 255'"
-        KERNEL=="nvidia_modeset", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia-modeset c $$(grep nvidia-frontend /proc/devices | cut -d \  -f 1) 254'"
+        KERNEL=="nvidia", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidiactl c 195 255'"
+        KERNEL=="nvidia_modeset", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia-modeset c 195 254'"
         KERNEL=="card*", SUBSYSTEM=="drm", DRIVERS=="nvidia", PROGRAM="${pkgs.gnugrep}/bin/grep 'Device Minor:' /proc/driver/nvidia/gpus/%b/information", \
-          RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia%c{3} c $$(grep nvidia-frontend /proc/devices | cut -d \  -f 1) %c{3}"
+          RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia%c{3} c 195 %c{3}"
         KERNEL=="nvidia_uvm", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia-uvm c $$(grep nvidia-uvm /proc/devices | cut -d \  -f 1) 0'"
         KERNEL=="nvidia_uvm", RUN+="${pkgs.runtimeShell} -c 'mknod -m 666 /dev/nvidia-uvm-tools c $$(grep nvidia-uvm /proc/devices | cut -d \  -f 1) 0'"
       '' + optionalString cfg.powerManagement.finegrained ''