drm/amd/display: Remove superflous error message

[Why]
VBios sometimes reports incorrect object type as encoder instead of
connector

[How]
Change error message to debug message

Signed-off-by: Jordan Lazare <Jordan.Lazare@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>