aomcx.h,cosmetics: sync AV1E_SET_CDF_UPDATE_MODE docs
aomcx.h,cosmetics: sync AV1E_SET_CDF_UPDATE_MODE docs

valid range is 0-2 with the meaning of 2 changing from 50% update to
selective update

Change-Id: I0dc5c0870b60595e2fdb3f463833205416bc697b

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