drm/amd/display: correct log message for lttpr

[Why]
When setting lttpr mode, the new mode to bet is not logged properly.

[How]
Update log message to show the right mode.

Signed-off-by: abdoulaye berthe <abdoulaye.berthe@amd.com>
Reviewed-by: George Shen <George.Shen@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>