Fix the build with nasm.
Fix the build with nasm.

Use eax instead of rax.

BUG=aomedia:546

Change-Id: Ie3f704557d428d84531311a6bc690293465a622c

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