[U-Boot] u-boot-video failure in ut dm video_ansi

Anatolij,

The latest changes in u-boot-video.git master branch break the "ut dm video_ansi" unit test:

=> ut dm video_ansi Test: dm_test_video_ansi: video.c /var/lib/jenkins/workspace/u-boot-denx_uboot_video-master-build/src/u-boot/test/dm/video.c:186, dm_test_video_ansi(): 272 == compress_frame_buffer(dev): Expected 272, got 274 Failures: 1

This is a new failure in the last 8 commits or so; the previous push earlier today did not have this issue.