Address review comments
Address review comments

Signed-off-by: Xiaofei Bai <71227f671a5e0108fac5dafb06eb9757f327cbe4@arm.com>

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