Adapt to the new key allocation mechanism

diff --git a/include/mbedtls/cipher_internal.h b/include/mbedtls/cipher_internal.h
index 6687b36..d711339 100644
--- a/include/mbedtls/cipher_internal.h
+++ b/include/mbedtls/cipher_internal.h
@@ -137,7 +137,7 @@
 typedef struct
 {
     psa_algorithm_t alg;
-    psa_key_slot_t slot;
+    psa_key_handle_t slot;
     mbedtls_cipher_psa_key_ownership slot_state;
 } mbedtls_cipher_context_psa;
 #endif /* MBEDTLS_USE_PSA_CRYPTO */