drm/amd/display: fix return value check for hdcp_work

max_caps might be 0, thus hdcp_work might be ZERO_SIZE_PTR
Signed-off-by: Flora Cui <flora.cui@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_hdcp.c

@@ -604,7 +604,7 @@ struct hdcp_workqueue *hdcp_create_workqueue(struct amdgpu_device *adev, struct
 	int i = 0;
 
 	hdcp_work = kcalloc(max_caps, sizeof(*hdcp_work), GFP_KERNEL);
-	if (hdcp_work == NULL)
+	if (ZERO_OR_NULL_PTR(hdcp_work))
 		return NULL;
 
 	hdcp_work->srm = kcalloc(PSP_HDCP_SRM_FIRST_GEN_MAX_SIZE, sizeof(*hdcp_work->srm), GFP_KERNEL);