Replace ssl->handshake with handshake in write_cookie_ext()
Replace ssl->handshake with handshake in write_cookie_ext()

Signed-off-by: XiaokangQian <7b6134ba682adad72773df97eb8737186a67b798@arm.com>

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