instead of casting int to int64, pass the int
and use %w modifier to use the word version of the register.

TBR=kjellander@chromium.org
BUG=libyuv:706
TEST=git cl lint
R=wangcheng@google.com

Change-Id: Iee5a70f04d928903ca8efac00066b8821a465e36
Reviewed-on: https://chromium-review.googlesource.com/528381Reviewed-by: Cheng Wang <wangcheng@google.com>
Reviewed-by: Frank Barchard <fbarchard@google.com>