drm/amd/display: Round KHz up when calculating clock requests

[Why]
When requesting clocks from SMU which takes MHz inputs, DC will round
down KHz when converting to MHz, thus potentially requesting too low a
clock value.

[How]
Round up (ceil) when converting KHz to MHz for clock requests to SMU.

Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>