page_server_async_read: fix pr_perror usage

Le sigh.

travis-ci: success for more pr_perror() usage fixes
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/page-xfer.c

@@ -1014,7 +1014,7 @@ int page_server_async_read(void)
 
 	ret = recv(page_server_sk, buf, need, MSG_DONTWAIT);
 	if (ret < 0) {
-		pr_perror("Error reading async data from page server\n");
+		pr_perror("Error reading async data from page server");
 		return -1;
 	}