lilypond-with-fonts: fix typos

In development, I experimented with file globs, for loops and making the
supplementary fonts optional. As such, the original PR ended up with a
dysfunctional combination.

This commit fully adopts the for loop approach, which I prefer, since failing
matches, e.g. missing supplementary-fonts/, won't cause a failure.

pkgs/misc/lilypond/fonts.nix

@@ -24,11 +24,11 @@ let
 
       installPhase = ''
         for f in {otf,supplementary-fonts}/**.{o,t}tf; do
-          install -Dt $out/otf -m755 otf/*
+          install -Dt $out/otf -m755 $f
         done
 
         for f in svg/**.{svg,woff}; do
-          install -Dt $out/svg -m755 svg/*
+          install -Dt $out/svg -m755 $f
         done
       '';