drm/amd/display: program v_update and v_ready with proper field

drm/amd/display: program v_update and v_ready with proper field

[WHY]
There are two different variables used to calculate v_update and v_ready,
one for validation and the other for performance parameter calculation.
Before the variable for validation was used which caused underflow on
1080edp with vsr enabled

[HOW]
program v_update and v_ready with the variables for performance parameter
calculation

Signed-off-by: Su Sung Chung <su.chung@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>