drm/amd/display: Fix visual confirm color not updating

[WHY]
Sometimes visual confirm color is updated, but the
background color is not changed. This causes visual
confrim to show incorrect colors.

[HOW]
Update background color when visual confirm color changes.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Leo Zeng <Leo.Zeng@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>