mfd: Fix bus lock interaction for WM831x IRQ set_type() operation

The WM831x IRQ set_type() operation is doing a direct register write when
called but since set_type() is called with the bus lock held this isn't
legal and could cause deadlocks in the IRQ core.

Fix this by posting the updates into an array and syncing in the
bus_sync_unlock() callback.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>