Fix compiler warning in od_dering.c.
Fix compiler warning in od_dering.c.

Change-Id: I4616af430ebbe43ced6f91ccf67a4fc0f40ba3bf

mbebenita/aom,smarter/aom,smarter/aom,mbebenita/aom,luctrudeau/aom,shacklettbp/aom,jmvalin/aom,GrokImageCompression/aom,luctrudeau/aom,jmvalin/aom,mbebenita/aom,mbebenita/aom,thdav/aom,thdav/aom,mbebenita/aom,smarter/aom,smarter/aom,shacklettbp/aom,shacklettbp/aom,GrokImageCompression/aom,luctrudeau/aom,luctrudeau/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,thdav/aom,luctrudeau/aom,mbebenita/aom,luctrudeau/aom,jmvalin/aom,thdav/aom,mbebenita/aom,smarter/aom,mbebenita/aom,shacklettbp/aom,thdav/aom,thdav/aom,jmvalin/aom,shacklettbp/aom,smarter/aom,jmvalin/aom,jmvalin/aom,shacklettbp/aom,GrokImageCompression/aom,mbebenita/aom