nixos/nvidia: fix type of bus ID option to accept empty string

nixos/modules/hardware/video/nvidia.nix

@@ -24,6 +24,7 @@ let
   primeEnabled = syncCfg.enable || offloadCfg.enable;
   nvidiaPersistencedEnabled =  cfg.nvidiaPersistenced;
   nvidiaSettings = cfg.nvidiaSettings;
+  busIDType = types.strMatching "([[:print:]]+\:[0-9]{1,3}\:[0-9]{1,2}\:[0-9])?";
 in
 
 {
@@ -68,7 +69,7 @@ in
     };
 
     hardware.nvidia.prime.nvidiaBusId = mkOption {
-      type = types.strMatching "[[:print:]]+\:[0-9]{1,3}\:[0-9]{1,2}\:[0-9]";
+      type = busIDType;
       default = "";
       example = "PCI:1:0:0";
       description = ''
@@ -78,7 +79,7 @@ in
     };
 
     hardware.nvidia.prime.intelBusId = mkOption {
-      type = types.strMatching "[[:print:]]+\:[0-9]{1,3}\:[0-9]{1,2}\:[0-9]";
+      type = busIDType;
       default = "";
       example = "PCI:0:2:0";
       description = ''
@@ -88,7 +89,7 @@ in
     };
 
     hardware.nvidia.prime.amdgpuBusId = mkOption {
-      type = types.strMatching "[[:print:]]+\:[0-9]{1,3}\:[0-9]{1,2}\:[0-9]";
+      type = busIDType;
       default = "";
       example = "PCI:4:0:0";
       description = ''