drm/amd/display: Fix DMUB debugging print issue

[Why]
The DMUB diagnostic data was not printed out correctly.

[How]
Print the DMUB diagnostic data line by line.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Cruise Hung <cruise.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>