drm/radeon/kms: Hide debugging message

Use the proper macro to issue the debugging message in
radeon_atif_call(). Otherwise we spam the log of many systems with a
message which looks like an error message of unknown origin, and could
thus confuse the user. Commit dc77de12
was a first step in this direction, but was not sufficient IMHO.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>