kata-ctl: Allow unused enum field

Clippy errors with:
```
error: field `0` is never read
```
but the field is required for the `map_err`, so ignore this
error for now to avoid too much disruption

Signed-off-by: stevenhorsman <steven@uk.ibm.com>

src/tools/kata-ctl/src/ops/exec_ops.rs

@@ -46,6 +46,7 @@ macro_rules! sl {
 }
 
 #[derive(Debug)]
+#[allow(dead_code)]
 pub enum Error {
     EpollWait(io::Error),
     EpollCreate(io::Error),