drm/amd/display: Skip override for preferred link settings during link training

[Why]
Overriding link setting inside override_training_settings
result in fallback link settings being ignored. This can
potentially cause link training to always fail and consequently
result in an infinite loop of link training to occur in
dp_verify_link_cap during detection.

[How]
Since preferred link settings are already considered inside
decide_link_settings, skip the check in override_training_settings
to avoid infinite link training loops.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>