Introduce PSA_KEY_HANDLE_INIT macro

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 54cdd7d..16bd619 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -1207,7 +1207,7 @@
     const char *pers = "ssl_client2";
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
-    psa_key_handle_t slot = 0;
+    psa_key_handle_t slot = PSA_KEY_HANDLE_INIT;
     psa_algorithm_t alg = 0;
     psa_key_attributes_t key_attributes;
     psa_status_t status;
@@ -1232,7 +1232,7 @@
     mbedtls_x509_crt clicert;
     mbedtls_pk_context pkey;
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
-    psa_key_handle_t key_slot = 0; /* invalid key slot */
+    psa_key_handle_t key_slot = PSA_KEY_HANDLE_INIT; /* invalid key slot */
 #endif
 #endif
     char *p, *q;
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index ec3d6ad..c11b081 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -1795,7 +1795,7 @@
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_algorithm_t alg = 0;
-    psa_key_handle_t psk_slot = 0;
+    psa_key_handle_t psk_slot = PSA_KEY_HANDLE_INIT;
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
     unsigned char psk[MBEDTLS_PSK_MAX_LEN];
     size_t psk_len = 0;