Pekka Paalanen authored Oct 10, 2022 and Pekka Paalanen committed Dec 02, 2022

Only the 'image' field of struct buffer is ever used here, so just
pass pixman_image_t instead of struct buffer.

This allows a future test to mangle a screenshot (e.g. convert pixel
format) before feeding it in.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>