V4L/DVB (12369): stv680: kfree called before usb_kill_urb

The irq handler will touch memory. Even in the error case some URBs may
complete. Thus no memory must be kfreed before all URBs are killed.

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>