psa: example: Initialize operation contexts

Add missing initializers to PSA Crypto example. Operation contexts must
be initialized before calling psa_*_setup().
diff --git a/programs/psa/crypto_examples.c b/programs/psa/crypto_examples.c
index 9947a70..0908756 100644
--- a/programs/psa/crypto_examples.c
+++ b/programs/psa/crypto_examples.c
@@ -109,7 +109,7 @@
                                     size_t *output_len )
 {
     psa_status_t status;
-    psa_cipher_operation_t operation;
+    psa_cipher_operation_t operation = PSA_CIPHER_OPERATION_INIT;
     size_t iv_len = 0;
 
     memset( &operation, 0, sizeof( operation ) );
@@ -140,7 +140,7 @@
                                     size_t *output_len )
 {
     psa_status_t status;
-    psa_cipher_operation_t operation;
+    psa_cipher_operation_t operation = PSA_CIPHER_OPERATION_INIT;
 
     memset( &operation, 0, sizeof( operation ) );
     status = psa_cipher_decrypt_setup( &operation, key_handle, alg );