Attest: Rename useful_buf to q_useful_buf

Set proper namespace to indicate that q_usful_buf
is originated from QCBOR library and to prevent
namespace collison.

Change-Id: I00a10ccc052dd4d4757f1c451d6534385e58ef00
Signed-off-by: Laurence Lundblade <lgl@securitytheory.com>
Co-authored-by: Tamas Ban <tamas.ban@arm.com>
diff --git a/lib/t_cose/inc/t_cose_common.h b/lib/t_cose/inc/t_cose_common.h
index d509a4b..1459702 100644
--- a/lib/t_cose/inc/t_cose_common.h
+++ b/lib/t_cose/inc/t_cose_common.h
@@ -12,6 +12,9 @@
 #ifndef __T_COSE_COMMON_H__
 #define __T_COSE_COMMON_H__
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /**
  * \file t_cose_common.h
@@ -143,6 +146,9 @@
     T_COSE_ERR_SHORT_CIRCUIT_SIG
 };
 
+#ifdef __cplusplus
+}
+#endif
 
 
 #endif /* __T_COSE_COMMON_H__ */