wm831x_power: Use IRQF_ONESHOT to request threaded IRQs

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.

scripts/coccinelle/misc/irqf_oneshot.cocci detected this issue.

Fixes: b5874f33 ("wm831x_power: Use genirq")
Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>