Improve/fix documentation

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/psa_crypto_slot_management.h b/library/psa_crypto_slot_management.h
index 8b9d746..ef0814a 100644
--- a/library/psa_crypto_slot_management.h
+++ b/library/psa_crypto_slot_management.h
@@ -79,9 +79,9 @@
  *                      identified by \p key.
  *
  * \retval #PSA_SUCCESS
- *         The pointer to the key slot containing the description of the key
- *         identified by \p key was returned. The key slot counter was
- *         implemented.
+ *         \p *p_slot contains a pointer to the key slot containing the
+ *         description of the key identified by \p key.
+ *         The key slot counter has been incremented.
  * \retval #PSA_ERROR_BAD_STATE
  *         The library has not been initialized.
  * \retval #PSA_ERROR_INVALID_HANDLE