drm/amd/display: Fix NULL pointer dereference at hibernate

During hibernate sequence the source context might not have a clk_mgr.
So don't use it to look for DML2 support.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2980
Fixes: 7966f319 ("drm/amd/display: Introduce DML2")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -4554,7 +4554,7 @@ void dc_resource_state_copy_construct(
 	struct dml2_context *dml2 = NULL;
 
 	// Need to preserve allocated dml2 context
-	if (src_ctx->clk_mgr->ctx->dc->debug.using_dml2)
+	if (src_ctx->clk_mgr && src_ctx->clk_mgr->ctx->dc->debug.using_dml2)
 		dml2 = dst_ctx->bw_ctx.dml2;
 #endif
 
@@ -4562,7 +4562,7 @@ void dc_resource_state_copy_construct(
 
 #ifdef CONFIG_DRM_AMD_DC_FP
 	// Preserve allocated dml2 context
-	if (src_ctx->clk_mgr->ctx->dc->debug.using_dml2)
+	if (src_ctx->clk_mgr && src_ctx->clk_mgr->ctx->dc->debug.using_dml2)
 		dst_ctx->bw_ctx.dml2 = dml2;
 #endif