mumble: Add correct dependency for use-speex option

Support for the speex codec has long since been removed from upstream.

See https://github.com/mumble-voip/mumble/pull/5869 for details.

the use-bundled-speex option now means to use the speex-dsp library
which is packaged separately in nix.

pkgs/applications/networking/mumble/default.nix

@@ -10,8 +10,8 @@
   boost,
   libopus,
   libsndfile,
+  speexdsp,
   protobuf,
-  speex,
   libcap,
   alsa-lib,
   python3,
@@ -103,6 +103,7 @@ let
           libopus
           libsndfile
           libvorbis
+          speexdsp
           qt5.qtsvg
           rnnoise
         ]