psa: Call init when importing private EC keys

Previously we weren't initializing the freshly allocated ECP keypair
when importing private EC keys. This didn't seem to cause problems, at
least according to our current test coverage, but it's better to ensure
we don't have a partially initialized object by explicitly initializing
the keypair.

Author: Patater

library/psa_crypto.c

@@ -572,6 +572,7 @@ static psa_status_t psa_import_ec_private_key( psa_ecc_curve_t curve,
     ecp = mbedtls_calloc( 1, sizeof( mbedtls_ecp_keypair ) );
     if( ecp == NULL )
         return( PSA_ERROR_INSUFFICIENT_MEMORY );
+    mbedtls_ecp_keypair_init( ecp );
 
     /* Load the group. */
     status = mbedtls_to_psa_error(