Added PSA_ERROR_STORAGE_FAILURE to psa_mac_compute

In case the key could not be retrieved from
storage.
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index a797cd5..de79c9b 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -1134,6 +1134,8 @@
  * \retval #PSA_ERROR_COMMUNICATION_FAILURE
  * \retval #PSA_ERROR_HARDWARE_FAILURE
  * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_STORAGE_FAILURE
+ *         The key could not be retrieved from storage.
  * \retval #PSA_ERROR_BAD_STATE
  *         The library has not been previously initialized by psa_crypto_init().
  *         It is implementation-dependent whether a failure to initialize