Trousers: fix missing include in trousers.h

BUG=b:147611033
TEST=build OK.

Change-Id: I6b519d6380fd5c9b92cd977c03b8994e032a08ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/trousers/+/1997520
Tested-by: Leo Lai <cylai@google.com>
Commit-Queue: Leo Lai <cylai@google.com>
Reviewed-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
diff --git a/src/include/trousers/trousers.h b/src/include/trousers/trousers.h
index 6b1f106..fe25ee2 100644
--- a/src/include/trousers/trousers.h
+++ b/src/include/trousers/trousers.h
@@ -11,6 +11,8 @@
 #ifndef _TROUSERS_H_
 #define _TROUSERS_H_
 
+#include <trousers/tss.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif