Use pixel stride of 2 for Y422_I's Y plane

Y422_I's layout is: Y0 Cr0 Y1 Cb0 ...

...which means that successive luminance samples are separated by 2
bytes, not 1.

Bug: 351311764
Test: builds
Flag: EXEMPT bugfix
Change-Id: I4c24aae97ef052f6385281dd6e73f748d880decb