drm/amdgpu/dm: Do not throw an error for a display with no audio

drm/amdgpu/dm: Do not throw an error for a display with no audio

An old display with no audio may not have an EDID with a CEA block, or
it may simply be too old to support audio. This is not a driver error,
so don't flag it as such.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112140
References: 997086e89422 ("drm/amd: be quiet when no SAD block is found")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Jean Delvare <jdelvare@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>