mkv: cleanup of matroska_segment_c::ParseTrackEntry

A few more lines, but far easier to read; and we should definitely
prefer maintainability instead of striving for just as few LOCs as
possible.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/matroska_segment_parse.cpp

@@ -596,7 +596,10 @@ void matroska_segment_c::ParseTrackEntry( KaxTrackEntry *m )
         }
         E_CASE( KaxAudioSamplingFreq, afreq )
         {
-            vars.tk->i_original_rate = vars.tk->fmt.audio.i_rate = static_cast<float>( afreq );
+            float const value = static_cast<float>( afreq );
+
+            vars.tk->i_original_rate  = value;
+            vars.tk->fmt.audio.i_rate = value;
             debug( vars, "afreq=%d", vars.tk->fmt.audio.i_rate ) ;
         }
         E_CASE( KaxAudioOutputSamplingFreq, afreq )