regmap: irq: initialize all irqs to wake disabled

The kerneldoc for irq_set_irq_wake() says:

    Enable/disable power management wakeup mode, which is
    disabled by default.

regmap_irq_set_wake() clears bits to enable wake for an interrupt,
and sets bits to disable wake. Hence, we should set all bits in
wake_buf initially, to mirror the expected disabled state.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>