request_threaded_irq() rejects calls which both do not specify a handler
(indicating that the primary IRQ handler should be used) and do not set
IRQF_ONESHOT because the combination is unsafe with level-triggered
interrupts.  It is safe in this case, though, since max98090 IRQs are
edge-triggered and the interrupts aren't ACK'ed until the codec's IRQ
status register is read.  Because of this, an IRQF_ONESHOT interrupt
doesn't really make a difference, but request one anyway in order to make
request_threaded_irq() happy.
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>