Fix inconsistency in variable declaration/use

The guards for the declaration and use were not consistent. This could
be resolved either way; I chose the way that matches development.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_psa_crypto_se_driver_hal.function b/tests/suites/test_suite_psa_crypto_se_driver_hal.function
index 485251e..2f1ffab 100644
--- a/tests/suites/test_suite_psa_crypto_se_driver_hal.function
+++ b/tests/suites/test_suite_psa_crypto_se_driver_hal.function
@@ -669,10 +669,8 @@
     psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
     psa_mac_operation_t mac_operation = PSA_MAC_OPERATION_INIT;
     psa_cipher_operation_t cipher_operation = PSA_CIPHER_OPERATION_INIT;
-#if defined(MBEDTLS_SHA256_C)
     psa_key_derivation_operation_t derivation_operation =
         PSA_KEY_DERIVATION_OPERATION_INIT;
-#endif
     uint8_t buffer[80]; /* large enough for a public key for ECDH */
     size_t length;
     mbedtls_svc_key_id_t key2 = MBEDTLS_SVC_KEY_ID_INIT;