mfd: si476x-i2c: Pass the IRQF_ONESHOT flag

Since commit 1c6c6952 ("genirq: Reject
bogus threaded irq requests") threaded IRQs without a primary handler
need to be requested with IRQF_ONESHOT, otherwise the request will fail.

So pass the IRQF_ONESHOT flag in this case.

The semantic patch that makes this change is available
in scripts/coccinelle/misc/irqf_oneshot.cocci.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>