added missing externs

Originally committed as revision 658 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegaudio.h

@@ -17,8 +17,8 @@
 
 int l2_select_table(int bitrate, int nb_channels, int freq, int lsf);
 
-const UINT16 mpa_bitrate_tab[2][3][15];
-const UINT16 mpa_freq_tab[3];
+extern const UINT16 mpa_bitrate_tab[2][3][15];
+extern const UINT16 mpa_freq_tab[3];
 extern const unsigned char *alloc_tables[5];
 extern const double enwindow[512];
 extern const int sblimit_table[5];