drm/amd/display: Fix BSOD with NULL check

[Why]
CLK mgr is null for server settings.

[How]
Guard the function with NULL check.
Signed-off-by: Chris Park <Chris.Park@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Wayne Lin <waynelin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -3274,7 +3274,7 @@ void dc_allow_idle_optimizations(struct dc *dc, bool allow)
 	if (dc->debug.disable_idle_power_optimizations)
 		return;
 
-	if (dc->clk_mgr->funcs->is_smu_present)
+	if (dc->clk_mgr != NULL && dc->clk_mgr->funcs->is_smu_present)
 		if (!dc->clk_mgr->funcs->is_smu_present(dc->clk_mgr))
 			return;