vtest: fix -Wstrict-prototypes build failure

Fixes: 7f644a81 ("Revert "meson: tighten up compile warnings with -Werror=all"")
Signed-off-by: Yiwei Zhang <zzyiwei@chromium.org>
Part-of: <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1165>
diff --git a/vtest/vtest_fuzzer.c b/vtest/vtest_fuzzer.c
index 7505f14..4b0f948 100644
--- a/vtest/vtest_fuzzer.c
+++ b/vtest/vtest_fuzzer.c
@@ -59,7 +59,7 @@
 #if __has_feature(address_sanitizer)
 const char* __lsan_default_suppressions(void);
 
-const char* __lsan_default_suppressions() {
+const char* __lsan_default_suppressions(void) {
    return "leak:dri2_initialize_surfaceless\n";
 }
 #endif // __has_feature(address_sanitizer)