Follow up on timing info

[andrey-norkin]

This is a follow-up on #5200.

Even after fixing the integer division, the result in incorrect.
The DispCT is now defined in the code as

display_clock_tick =
(double) cm->ci_params_encoder.timing_info.num_ticks_per_elemental_duration /
cm->ci_params_encoder.timing_info.time_scale;

Whereas the spec correctly says:
DispCT = num_units_in_display_tick ÷ time_scale

This needs to be further fixed. Currently, it causes incorrect frame rates.