drm/amd/display: Fill plane attrs only for valid pxl format

[Why]
In fill_plane_buffer_attributes() we calculate chroma/luma
assuming that the surface_pixel_format is always valid.
If it's not the case, there's a risk of divide by zero error.

[How]
Check if format valid before calculating pixel format attributes

Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>