Change cert file to server2-sha256.crt
Change cert file to server2-sha256.crt

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

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