Refactor `psa_load_persistent_key_into_slot` to remove bad `goto`

Merges the two calls to `psa_copy_key_material_into_slot.

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index 5ecc3a7..0278009 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -234,14 +234,10 @@
             status = PSA_ERROR_DATA_INVALID;
             goto exit;
         }
-        data = (psa_se_key_data_storage_t *) key_data;
-        status = psa_copy_key_material_into_slot(
-            slot, data->slot_number, sizeof(data->slot_number));
 
-        if (status == PSA_SUCCESS) {
-            slot->status = PSA_SLOT_OCCUPIED;
-        }
-        goto exit;
+        data = (psa_se_key_data_storage_t *) key_data;
+        key_data = data->slot_number;
+        key_data_length = sizeof(key_data);
     }
 #endif /* MBEDTLS_PSA_CRYPTO_SE_C */