gpio: pcf857x: call the gpio user handler iff gpio_to_irq is done

For pcf857x driver if the initial state is not set properly (proper
n_latch is not passed), we get bad irq prints on console.
We get this only for the first interrupt and doesnot repeat for further
interrupts unles and until there are other gpio pins which are not flipping
continously.

following prints are seen on console.

[   40.983924] irq 0, desc: ce004080, depth: 1, count: 0, unhandled: 0
[   40.990511] ->handle_irq():  c00aa538, handle_bad_irq+0x0/0x260
[   40.996768] ->irq_data.chip(): c080b6ec, no_irq_chip+0x0/0x60
[   41.002842] ->action():   (null)
[   41.006242]    IRQ_NOPROBE set
[   41.009465]  IRQ_NOREQUEST set

Signed-off-by: George Cherian <george.cherian@ti.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>