libsigrok: take unversioned python argument

libsigrok can be built with different python versions which we want to
use for integrating it into python*Packages.

pkgs/development/tools/libsigrok/default.nix

@@ -1,5 +1,5 @@
 { lib, stdenv, fetchurl, pkg-config, libzip, glib, libusb1, libftdi1, check
-, libserialport, librevisa, doxygen, glibmm, python3
+, libserialport, librevisa, doxygen, glibmm, python
 , version ? "0.5.1", sha256 ? "171b553dir5gn6w4f7n37waqk62nq2kf1jykx4ifjacdz5xdw3z4", doInstallCheck ? true
 }:
 
@@ -17,7 +17,7 @@ stdenv.mkDerivation rec {
     sha256 = "14sd8xqph4kb109g073daiavpadb20fcz7ch1ipn0waz7nlly4sw";
   };
 
-  nativeBuildInputs = [ doxygen pkg-config python3 ];
+  nativeBuildInputs = [ doxygen pkg-config python ];
   buildInputs = [ libzip glib libusb1 libftdi1 check libserialport librevisa glibmm ];
 
   strictDeps = true;

pkgs/top-level/all-packages.nix

@@ -14529,9 +14529,12 @@ with pkgs;
 
   libstdcxx5 = callPackage ../development/libraries/gcc/libstdc++/5.nix { };
 
-  libsigrok = callPackage ../development/tools/libsigrok { };
+  libsigrok = callPackage ../development/tools/libsigrok {
+    python = python3;
+  };
   # old version:
   libsigrok_0_3 = libsigrok.override {
+    python = python3;
     version = "0.3.0";
     sha256 = "0l3h7zvn3w4c1b9dgvl3hirc4aj1csfkgbk87jkpl7bgl03nk4j3";
     doInstallCheck = false;