Input: hp680_ts_input - ensure arguments to request_irq and free_irq are compatible

Change 0 to NULL in the last argument of request_irq, since the argument
should have pointer type and so that the last argument of request_irq
syntactically matches the second argument of the later call to free_irq.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>