cryptsetup: fix build with -Db_ndebug=true

cryptsetup: fix build with -Db_ndebug=true

```
 ...
 ../src/cryptsetup/cryptsetup-tokens/cryptsetup-token-systemd-fido2.c:33:13: error: variable 'r' set but not used [-Werror,-Wunused-but-set-variable]
         int r;
             ^
 1 error generated.
 ...
 ../src/cryptsetup/cryptsetup-tokens/cryptsetup-token-systemd-pkcs11.c:34:13: error: variable 'r' set but not used [-Werror,-Wunused-but-set-variable]
         int r;
             ^
 1 error generated.
 ninja: build stopped: subcommand failed.
 + fatal ''\''meson compile'\'' failed with -Db_ndebug=true'
```