Fix compilation when the Sonic encoder and decoder were disabled and only the Sonic

LS encoder enabled.

Originally committed as revision 9093 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/Makefile

@@ -155,7 +155,7 @@ OBJS-$(CONFIG_SNOW_ENCODER)            += snow.o
 OBJS-$(CONFIG_SOL_DPCM_DECODER)        += dpcm.o
 OBJS-$(CONFIG_SONIC_DECODER)           += sonic.o
 OBJS-$(CONFIG_SONIC_ENCODER)           += sonic.o
-OBJS-$(CONFIG_SONIC_LS_DECODER)        += sonic.o
+OBJS-$(CONFIG_SONIC_LS_ENCODER)        += sonic.o
 OBJS-$(CONFIG_SP5X_DECODER)            += sp5xdec.o mjpegdec.o mjpeg.o
 OBJS-$(CONFIG_SVQ1_DECODER)            += svq1.o
 OBJS-$(CONFIG_SVQ1_ENCODER)            += svq1.o