drm/amd/display: Check null pointers before using them

[WHAT & HOW]
These pointers are null checked previously in the same function,
indicating they might be null as reported by Coverity. As a result,
they need to be checked when used again.

This fixes 3 FORWARD_NULL issue reported by Coverity.
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -7195,6 +7195,9 @@ create_validate_stream_for_sink(struct amdgpu_dm_connector *aconnector,
 	int requested_bpc = drm_state ? drm_state->max_requested_bpc : 8;
 	enum dc_status dc_result = DC_OK;
 
+	if (!dm_state)
+		return NULL;
+
 	do {
 		stream = create_stream_for_sink(connector, drm_mode,
 						dm_state, old_stream,
@@ -9302,7 +9305,7 @@ static void amdgpu_dm_commit_streams(struct drm_atomic_state *state,
 		if (acrtc)
 			old_crtc_state = drm_atomic_get_old_crtc_state(state, &acrtc->base);
 
-		if (!acrtc->wb_enabled)
+		if (!acrtc || !acrtc->wb_enabled)
 			continue;
 
 		dm_old_crtc_state = to_dm_crtc_state(old_crtc_state);
@@ -9706,9 +9709,10 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
 
 			DRM_INFO("[HDCP_DM] hdcp_update_display enable_encryption = %x\n", enable_encryption);
 
-			hdcp_update_display(
-				adev->dm.hdcp_workqueue, aconnector->dc_link->link_index, aconnector,
-				new_con_state->hdcp_content_type, enable_encryption);
+			if (aconnector->dc_link)
+				hdcp_update_display(
+					adev->dm.hdcp_workqueue, aconnector->dc_link->link_index, aconnector,
+					new_con_state->hdcp_content_type, enable_encryption);
 		}
 	}