nvme_test: update shadow doorbell handling to mirror nvme crate

Cargo.lock

@@ -4865,7 +4865,6 @@ dependencies = [
  "chipset_device",
  "device_emulators",
  "disk_backend",
- "event-listener",
  "futures",
  "futures-concurrency",
  "guestmem",

vm/devices/storage/nvme_test/Cargo.toml

@@ -27,7 +27,6 @@ inspect.workspace = true
 mesh.workspace = true
 pal_async.workspace = true
 async-trait.workspace = true
-event-listener.workspace = true
 futures.workspace = true
 futures-concurrency.workspace = true
 parking_lot.workspace = true

vm/devices/storage/nvme_test/src/pci.rs

@@ -233,15 +233,15 @@ impl NvmeFaultController {
         if addr >= 0x1000 {
             // Doorbell write.
             let base = addr - 0x1000;
-            let index = base >> DOORBELL_STRIDE_BITS;
-            if (index << DOORBELL_STRIDE_BITS) != base {
+            let db_id = base >> DOORBELL_STRIDE_BITS;
+            if (db_id << DOORBELL_STRIDE_BITS) != base {
                 return IoResult::Err(InvalidRegister);
             }
             let Ok(data) = data.try_into() else {
                 return IoResult::Err(IoError::InvalidAccessSize);
             };
-            let data = u32::from_ne_bytes(data);
-            self.workers.doorbell(index, data);
+            let value = u32::from_ne_bytes(data);
+            self.workers.doorbell(db_id, value);
             return IoResult::Ok;
         }