drm/amd/display: Don't log error if we have no connectors

[Why]
In certain configurations, such as PX configs or some Vega20 parts
DC gets created without connectors.

[How]
Drop the dm_error print when no connectors.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>