xorg.xf86videoati: Use dev output of xorgserver

TODO: Darwin xorgserver should have consistent outputs with the Linux
one.

pkgs/servers/x11/xorg/overrides.nix

···
   };
 
   xf86videoati = attrs: attrs // {
-    NIX_CFLAGS_COMPILE = "-I${xorg.xorgserver}/include/xorg";
+    NIX_CFLAGS_COMPILE = "-I${xorg.xorgserver.dev or xorg.xorgserver}/include/xorg";
   };
 
   xf86videonv = attrs: attrs // {