drm/amd/display: Update dmub header to match DMUB

[WHY]
Last PR missed name of a struct to match in DMUB

[HOW]
Update the logic in dmub_cmh.h header

Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Reviewed-by: Meenakshikumar Somasundaram <Meenakshikumar.Somasundaram@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Mustapha Ghaddar <mghaddar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>