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: Cao,Bing Bu <mars@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
