Fix build on --disable-avx2
Fix build on --disable-avx2

BUG=aomedia:536

Change-Id: I92c5e43ba225968504ff1c878ca80b86449aeefe

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom