usb: kill handle_packet callback

usb: kill handle_packet callback

All drivers except usb-hub use usb_generic_handle_packet.  The only
reason the usb hub has its own function is that it used to be called
with packets which are intended for downstream devices.  With the new,
separate device lookup step this doesn't happen any more, so the need
for a different handle_packet callback is gone.

So we can kill the handle_packet callback and just call
usb_generic_handle_packet directly.  The special hub handling in
usb_handle_packet() can go away for the same reason.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>