USB: make usb_iso_packet_descriptor.status signed

The status in usb_iso_packet_descriptor should be signed, for the benefit
of someone who casts to a long or makes other benign misstep (the principle
of least surprise).

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>