USB: Serial: omninet: Fix compiler warning.

I forgot to remove an unused variable.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/omninet.c

@@ -162,7 +162,6 @@ static void omninet_read_bulk_callback(struct urb *urb)
 	struct omninet_header 	*header = (struct omninet_header *) &data[0];
 	int status = urb->status;
 	int result;
-	int i;
 
 	if (status) {
 		dev_dbg(&port->dev, "%s - nonzero read bulk status received: %d\n",