Uses 1 add instead of 2 leas to reduce port pressure on ports 1 and 5
used for SIMD instructions.

BUG=libyuv:670
TEST=~/iaca-lin64/bin/iaca.sh -arch HSW out/Release/obj/libyuv/row_gcc.o

Change-Id: I3965ee5dcb49941a535efa611b5988d977f5b65c
Reviewed-on: https://chromium-review.googlesource.com/433391Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>