mailbox: pcc: Remove spurious IRQF_ONESHOT usage

The PCC code currently specifies IRQF_ONESHOT if the interrupt could
potentially be shared but doesn't actually use request_threaded_irq() and
the interrupt handler does not use IRQ_WAKE_THREAD so IRQF_ONESHOT is
never relevant. Since commit aef30c8d569c ("genirq: Warn about using
IRQF_ONESHOT without a threaded handler") specifying it has resulted in a
WARN_ON(), fix this by removing IRQF_ONESHOT.

Reported-by: Aishwarya TCV <Aishwarya.TCV@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>