psa: include: Fix comments

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/psa/crypto_driver_contexts.h b/include/psa/crypto_driver_contexts.h
index bee6895..81428a4 100644
--- a/include/psa/crypto_driver_contexts.h
+++ b/include/psa/crypto_driver_contexts.h
@@ -41,7 +41,7 @@
  * of both this file and the content of psa_crypto_driver_wrappers.c */
 
 typedef union {
-    unsigned dummy; /* Make sure this structure is always non-empty */
+    unsigned dummy; /* Make sure this union is always non-empty */
     mbedtls_psa_hash_operation_t mbedtls_ctx;
 #if defined(PSA_CRYPTO_DRIVER_TEST)
     mbedtls_transparent_test_driver_hash_operation_t test_driver_ctx;
@@ -49,7 +49,7 @@
 } psa_driver_hash_context_t;
 
 typedef union {
-    unsigned dummy; /* Make sure this structure is always non-empty */
+    unsigned dummy; /* Make sure this union is always non-empty */
     mbedtls_psa_cipher_operation_t mbedtls_ctx;
 #if defined(PSA_CRYPTO_DRIVER_TEST)
     mbedtls_transparent_test_driver_cipher_operation_t transparent_test_driver_ctx;