drm/amd/display: Add callback for update_soc_for_wm_a for dcn303

[Why&How]
Absense of this callback causes null pointer dereference.
Add the corresponding callback in dcn303 resources.

Fixes: 443dfba0 ("drm/amd/display: fix dcn3+ bw validation soc param update sequence")
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>