drm/amd/display: fixed dcn30+ underflow issue

[Why]
Observing underflow on dcn30+ system config at 4k144hz

[How]
We set the UCLK hardmax on AC/DC switch if softmax is enabled
and also on boot. While booting up the UCLK Hardmax is set
to softmax before the init sequence and the init sequence
resets the hardmax to UCLK max which enables P-state switching.
Just added a conditional check to avoid setting hardmax on init.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Ayush Gupta <ayugupta@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>