fuzz-bcd: silence warning about always-true comparison

Occurs with gcc-11.2.1-7.fc35.x86_64.

src/boot/efi/fuzz-bcd.c

@@ -21,6 +21,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         assert_se(p);
 
         char16_t *title = get_bcd_title(p, size);
-        assert_se(!title || char16_strlen(title) >= 0);
+        if (title)
+                (void) char16_strlen(title);
         return 0;
 }