subsurface: make build src name independent

(cherry picked from commit 133158ffde)

pkgs/applications/misc/subsurface/default.nix

@@ -20,7 +20,8 @@ let
     inherit version;
 
     src = subsurfaceSrc;
-    sourceRoot = "source/libdivecomputer";
+
+    prePatch = "cd libdivecomputer";
 
     nativeBuildInputs = [ autoreconfHook ];