drm/amd/display: pbn_div need be updated for hotplug event

link_rate sometime will be changed when DP MST connector hotplug, so
pbn_div also need be updated; otherwise, it will mismatch with
link_rate, causes no output in external monitor.

This is a backport to 6.7 and older.

Cc: [email protected]
Tested-by: Daniel Wheeler <[email protected]>
Reviewed-by: Jerry Zuo <[email protected]>
Acked-by: Rodrigo Siqueira <[email protected]>
Signed-off-by: Wade Wang <[email protected]>
Signed-off-by: Wayne Lin <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: Wayne Lin

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -6914,8 +6914,7 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder,
 	if (IS_ERR(mst_state))
 		return PTR_ERR(mst_state);
 
-	if (!mst_state->pbn_div)
-		mst_state->pbn_div = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link);
+	mst_state->pbn_div = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link);
 
 	if (!state->duplicated) {
 		int max_bpc = conn_state->max_requested_bpc;