Clarify case when high level error code is incorrect
Clarify case when high level error code is incorrect

Signed-off-by: Chris Jones <cbf609b812bf58762ceb89e8692559dbbe9149ea@arm.com>

ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls