drm/amd/display: Modify comments to match the code

[Why]
This line of code was modified. However, comments
remained unchanged. As a result, comments and code are
mismatching.

[How]
Modifying comments to reflect code. At the same time,
explaining why the value was changed from 200ms to
3000ms.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>