fixup! psa: Disallow use of invalid MAC contexts

Author: Patater

tests/suites/test_suite_psa_crypto.function

@@ -2230,7 +2230,7 @@ exit:
 /* BEGIN_CASE */
 void mac_operation_init( )
 {
-    const uint8_t input[1];
+    const uint8_t input[1] = { 0 };
 
     /* Test each valid way of initializing the object, except for `= {0}`, as
      * Clang 5 complains when `-Wmissing-field-initializers` is used, even
@@ -2461,8 +2461,6 @@ void mac_sign( int key_type_arg,
                                      actual_mac, mac_buffer_size,
                                      &mac_length ) );
 
-    /* Ensure double sign fails properly. */
-
     /* Compare with the expected value. */
     ASSERT_COMPARE( expected_mac->x, expected_mac->len,
                     actual_mac, mac_length );