drm/amd/display: Write REFCLK to 48MHz on DCN21

drm/amd/display: Write REFCLK to 48MHz on DCN21

[Why&How]
dccg21_init() calls dccg2_init() which hardcodes 100MHz refclk values
for MICROSECOND_TIME_BASE_DIV and MILLISECOND_TIME_BASE_DIV. DCN21
uses 48MHz refclk, so the wrong values corrupt DCCG timing and cause eDP
link training failure on cold boot.

Write the correct 48MHz values directly instead of calling dccg2_init().

v2:
Fixed typo

Fixes: e6e2b956fc81 ("drm/amd/display: Add missing DCCG register entries for DCN20-DCN316")
Reported-by: Max Chernoff <git@maxchernoff.ca>
Tested-by: Max Chernoff <git@maxchernoff.ca>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>