nvidia-x11: pass kernel.modDirVersion

pkgs/os-specific/linux/nvidia-x11/builder.sh

@@ -17,7 +17,6 @@ buildPhase() {
         # Create the module.
         echo "Building linux driver against kernel: $kernel";
         cd kernel
-        kernelVersion=$(cd $kernel/lib/modules && ls)
         sysSrc=$(echo $kernel/lib/modules/$kernelVersion/source)
         sysOut=$(echo $kernel/lib/modules/$kernelVersion/build)
         unset src # used by the nv makefile

pkgs/os-specific/linux/nvidia-x11/generic.nix

@@ -55,6 +55,7 @@ let
     outputDev = if libsOnly then null else "bin";
 
     kernel = if libsOnly then null else kernel.dev;
+    kernelVersion = if libsOnly then null else kernel.modDirVersion;
 
     hardeningDisable = [ "pic" "format" ];