align a stack array to prevent segfault
align a stack array to prevent segfault

BUG=aomedia:1383

Change-Id: I8c3de068fd158b4706b578f7609c8ef939364525

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