Fix parse of usb device description with multiple configurations

Changed From V1:
Use DPRINTF instead of fprintf,because it is not an error.

When testing ipod on QEMU by He Jie Xu<xuhj@linux.vnet.ibm.com>,qemu made a assertion.
We found that the ipod with 2 configurations,and the usb-linux did not parse the descriptor correctly.
The descr_len returned is the total length of the all configurations,not one configuration.
The older version will through the other configurations instead of skip,continue parsing the descriptor of interfaces/endpoints in other configurations,then went wrong.

This patch will put the configuration descriptor parse in loop outside and dispel the other configurations not requested.
Signed-off-by: NCao,Bing Bu <mars@linux.vnet.ibm.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

usb-linux.c

@@ -1141,15 +1141,18 @@ static int usb_linux_update_endp_table(USBHostDevice *s)
     length = s->descr_len - 18;
     i = 0;
 
-    if (descriptors[i + 1] != USB_DT_CONFIG ||
-        descriptors[i + 5] != s->configuration) {
-        fprintf(stderr, "invalid descriptor data - configuration %d\n",
-                s->configuration);
-        return 1;
-    }
-    i += descriptors[i];
-
     while (i < length) {
+        if (descriptors[i + 1] != USB_DT_CONFIG) {
+            fprintf(stderr, "invalid descriptor data\n");
+            return 1;
+        } else if (descriptors[i + 5] != s->configuration) {
+            DPRINTF("not requested configuration %d\n", s->configuration);
+            i += (descriptors[i + 3] << 8) + descriptors[i + 2];
+            continue;
+        }
+
+        i += descriptors[i];
+
         if (descriptors[i + 1] != USB_DT_INTERFACE ||
             (descriptors[i + 1] == USB_DT_INTERFACE &&
              descriptors[i + 4] == 0)) {