lsiutil: substituteInPlace in the patch phase instead of buildPhase

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

···
     sha256 = "sha256-aTi+EogY1aDWYq3anjRkjz1mzINVfUPQbOPHthxrvS4=";
   };
 
+  postPatch = ''
+    substituteInPlace lsiutil.c \
+      --replace /sbin/modprobe "${kmod}/bin/modprobe" \
+      --replace /bin/mknod "${coreutils}/bin/mknod"
+  '';
+
   buildPhase = ''
     runHook preBuild
 
-    substituteInPlace lsiutil.c \
-      --replace /sbin/modprobe "${kmod}/bin/modprobe" \
-      --replace /bin/mknod "${coreutils}/bin/mknod"
     gcc -Wall -O lsiutil.c -o lsiutil
 
     runHook postBuild