nixos/modules/hardware/video/nvidia: Fix incorrect reference to 'nvidiaSettings'

This patch fixes a bug caused by an incorrect reference to
'nvidiaSettings' rather than 'cfg.nvidiaSettings'. The bug caused
the system to not build when using the nvidia drivers.

Tested on my local machine.

nixos/modules/hardware/video/nvidia.nix

@@ -290,7 +290,7 @@ in
     hardware.opengl.extraPackages32 = optional offloadCfg.enable nvidia_x11.lib32;
 
     environment.systemPackages = [ nvidia_x11.bin ]
-      ++ optionals nvidiaSettings [ nvidia_x11.settings ]
+      ++ optionals cfg.nvidiaSettings [ nvidia_x11.settings ]
       ++ optionals nvidiaPersistencedEnabled [ nvidia_x11.persistenced ];
 
     systemd.packages = optional cfg.powerManagement.enable nvidia_x11.out;