drm/amd/display: Change "error" to "dc_log" at amdgpu_dm dpcd reading stage

[Why]
If reading dpcd happens ahead of hw initialization, then aconnector is NULL
at this point. This is expected, so there is no need to output an error (which will
spam dmesg.log)

[How]
Change type of message from "error" to "DC_LOG_DC".
Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Zhan Liu <zhan.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -445,7 +445,7 @@ bool dm_helpers_dp_read_dpcd(
 	struct amdgpu_dm_connector *aconnector = link->priv;
 
 	if (!aconnector) {
-		DRM_ERROR("Failed to find connector for link!");
+		DC_LOG_DC("Failed to find connector for link!\n");
 		return false;
 	}