drm/amd/display: Reduce height of visual confirm on right side.

[Why]
right side visual confirm is too thick due to it is 4 times of
left side (16 lines).

[How]
Change factor from 4 to 2.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>