[devmgr][component] Fix proxying PDevGetInterrupt()

The index was not being passed.

Change-Id: I6060ff82a38bea0983c49bf234f6df30eb6016b5
diff --git a/zircon/system/core/devmgr/component/component-proxy.cpp b/zircon/system/core/devmgr/component/component-proxy.cpp
index 87f299a..133da53 100644
--- a/zircon/system/core/devmgr/component/component-proxy.cpp
+++ b/zircon/system/core/devmgr/component/component-proxy.cpp
@@ -388,6 +388,7 @@
     PdevProxyResponse resp = {};
     req.header.proto_id = ZX_PROTOCOL_PDEV;
     req.op = PdevOp::GET_INTERRUPT;
+    req.index = index;
     req.flags = flags;
 
     return Rpc(&req.header, sizeof(req), &resp.header, sizeof(resp), nullptr, 0,