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/hw/usb-msd.c b/hw/usb-msd.c
index bb39b62..b9f6588 100644
--- a/hw/usb-msd.c
+++ b/hw/usb-msd.c
@@ -600,6 +600,7 @@
 }
 
 static struct USBDeviceInfo msd_info = {
+    .product_desc   = "QEMU USB MSD",
     .qdev.name      = "QEMU USB MSD",
     .qdev.alias     = "usb-storage",
     .qdev.size      = sizeof(MSDState),