Improve psa_generate_key_internal()
Improve psa_generate_key_internal()

Small improvements to psa_generate_key_internal()
implementation:
. declare only once the status local variable and
  initialize it to PSA_ERROR_CORRUPTION_DETECTED
  to improve robustness against FI attacks.
. remove an unnecessary assignment.
. use type local variable instead of its global
  variable equivalent.

Signed-off-by: Ronald Cron <b35ff5b7ca26c4ae9b66b92f2cf34224c8e26b08@arm.com>

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