linuxPackages.{xpadneo, xone}: fix after simplifying sourceRoot

This partially reverts commits 68be474e30887a66e0530edfc898b74fb5dd5d26
and 5a0f953d9ffe5c40df263ccccffa647a86729f5a.

pkgs/os-specific/linux/xone/default.nix

···
     })
   ];
 
-  sourceRoot = src.name;
+  setSourceRoot = ''
+    export sourceRoot=$(pwd)/${src.name}
+  '';
 
   nativeBuildInputs = kernel.moduleBuildDependencies;
 

pkgs/os-specific/linux/xpadneo/default.nix

···
     sha256 = "sha256-rT2Mq40fE055FemDG7PBjt+cxgIHJG9tTjtw2nW6B98=";
   };
 
-  sourceRoot = "${finalAttrs.src.name}/hid-xpadneo/src";
+  setSourceRoot = ''
+    export sourceRoot=$(pwd)/${finalAttrs.src.name}/hid-xpadneo/src
+  '';
 
   nativeBuildInputs = kernel.moduleBuildDependencies;
   buildInputs = [ bluez ];