drm/amd/display: Fix DCFCLK and SOCCLK not set

[Why]
If voltage level > 0, DCFCLK and SOCCLK could be 0 during DML
calculations, which ended up causing an assert.

[How]
Initialize dcfclk_mhz and socclk_mhz values according to the
voltage level.

Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>