drm/amd/display: avoid printing ERROR for unknown CEA parse(v2)

For the unknown CEA parse case on DMUB-enabled ASICs, dmesg will
print an error message like below, this will be captured by
automation tools as it has the word like ERROR during boot up
and treated as a false error, as it does not break bootup process.
So use DRM_WARN printing for this.

[drm:amdgpu_dm_update_freesync_caps [amdgpu]] *ERROR* Unknown EDID CEA parser results

v2: Use DRM_WARN to print such info.

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Stylon Wang <stylon.wang@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>