Extend psa_wipe_key_slot documentation

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/library/psa_crypto_core.h b/library/psa_crypto_core.h
index 376337e..b5b9c54 100644
--- a/library/psa_crypto_core.h
+++ b/library/psa_crypto_core.h
@@ -190,7 +190,10 @@
  *         The slot has been successfully wiped.
  * \retval #PSA_ERROR_CORRUPTION_DETECTED
  *         The slot's state was PSA_SLOT_FULL or PSA_SLOT_PENDING_DELETION, and
- *         the amount of registered readers was not equal to 1.
+ *         the amount of registered readers was not equal to 1. Or,
+ *         the slot's state was PSA_SLOT_EMPTY. Or,
+ *         the slot's state was PSA_SLOT_FILLING, and the amount
+ *         of registered readers was not equal to 0.
  */
 psa_status_t psa_wipe_key_slot(psa_key_slot_t *slot);