tests/qtests: clean-up and fix leak in generic_fuzz

An update to the clang tooling detects more issues with the code
including a memory leak from the g_string_new() allocation. Clean up
the code to avoid the allocation and use ARRAY_SIZE while we are at
it.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230630180423.558337-9-alex.bennee@linaro.org>

tests/qtest/fuzz/generic_fuzz.c

@@ -954,17 +954,10 @@ static void register_generic_fuzz_targets(void)
             .crossover = generic_fuzz_crossover
     });
 
-    GString *name;
-    const generic_fuzz_config *config;
-
-    for (int i = 0;
-         i < sizeof(predefined_configs) / sizeof(generic_fuzz_config);
-         i++) {
-        config = predefined_configs + i;
-        name = g_string_new("generic-fuzz");
-        g_string_append_printf(name, "-%s", config->name);
+    for (int i = 0; i < ARRAY_SIZE(predefined_configs); i++) {
+        const generic_fuzz_config *config = predefined_configs + i;
         fuzz_add_target(&(FuzzTarget){
-                .name = name->str,
+                .name = g_strconcat("generic-fuzz-", config->name, NULL),
                 .description = "Predefined generic-fuzz config.",
                 .get_init_cmdline = generic_fuzz_predefined_config_cmdline,
                 .pre_fuzz = generic_pre_fuzz,