staging: pi433: fix interrupt handler signatures

Remove "struct pt_regs *" parameter from interrupt handlers, since
it is no longer passed to interrupt handlers. Also, convert return
types to irqreturn_t.

Additionally, move DIO_irq_handler variable into the setup_GPIO
function, as it's not used outside of this function.

Signed-off-by: Cihangir Akturk <cakturk@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>