qdev: Separate USB product description from qdev name

Using the qdev name for the product description makes for inconvenient
qdev names.

Put the product description in new USBDeviceInfo member product_desc.
Make usb_qdev_init() use it.  No user or guest visible change, since
the value is still the same.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/usb-bsd.c b/usb-bsd.c
index a9987d1..e72d123 100644
--- a/usb-bsd.c
+++ b/usb-bsd.c
@@ -393,6 +393,7 @@
 }
 
 static struct USBDeviceInfo usb_host_dev_info = {
+    .product_desc   = "USB Host Device",
     .qdev.name      = "USB Host Device",
     .qdev.size      = sizeof(USBHostDevice),
     .init           = usb_host_initfn,