[PATCH] USB: usbcore: usb_set_configuration oops (NULL ptr dereference)

When trying to deconfigure a device via usb_set_configuration(dev, 0),
2.6.16-rc kernels after 55c52718 oops
with "Unable to handle NULL pointer dereference at...". This is due to
an unchecked dereference of cp in the power budget part.

Signed-off-by: Horst Schirmeier <horst@schirmeier.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>