I422ToRGB24 is implemented as a C wrapper for Intel, calling
I422ToARGB and ARGBToRGB24.  The ARGBToRGB24 for AVX2 requires 32
pixels.
This CL increases the width alignment required to use I422ToRGB24_AVX2

TBR=rrwinterton0gmail.com

Bug: libyuv:822, b:118386049
Change-Id: I4454f4eece33fbd5f593655f577c9ef5c00d1f63
Tested: locally tested with app that crashed using this function.
Reviewed-on: https://chromium-review.googlesource.com/c/1299931Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>