SUNRPC: fix uninitialized variable warning

Avoid following compiler warning on uninitialized variable

net/sunrpc/xprtsock.c: In function ‘xs_read_stream_request.constprop’:
net/sunrpc/xprtsock.c:525:10: warning: ‘read’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   return read;
          ^~~~
net/sunrpc/xprtsock.c:529:23: warning: ‘ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ret < 0 ? ret : read;
         ~~~~~~~~~~~~~~^~~~~~
Signed-off-by: NAlakesh Haloi <alakesh.haloi@gmail.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/xprtsock.c

@@ -495,8 +495,8 @@ xs_read_stream_request(struct sock_xprt *transport, struct msghdr *msg,
 		int flags, struct rpc_rqst *req)
 {
 	struct xdr_buf *buf = &req->rq_private_buf;
-	size_t want, read;
-	ssize_t ret;
+	size_t want, uninitialized_var(read);
+	ssize_t uninitialized_var(ret);
 
 	xs_read_header(transport, buf);