virtio-devices: Remove panic when duplicating activate EventFds

Replace the (unlikely) panic when duplicating the EventFds with a
propagated error.

Signed-off-by: Rob Bradford <rbradford@meta.com>

virtio-devices/src/mem.rs

@@ -951,7 +951,7 @@ impl VirtioDevice for Mem {
             device_status,
         } = context;
         self.common.activate(&queues, interrupt_cb.clone())?;
-        let (kill_evt, pause_evt) = self.common.dup_eventfds();
+        let (kill_evt, pause_evt) = self.common.dup_eventfds()?;
 
         let (_, queue, queue_evt) = queues.remove(0);