mfd: madera: Add irqchip data pointer into struct madera

Put the pointer to struct regmap_irq_chip_data into the parent
mfd structure so that the child irqchip driver does not need
a trivial private structure to store only this pointer. As
the irqchip child driver already has a pointer to the parent
struct madera it can use that to store the pointer. This also
means that the irqchip driver does not need a double-indirection
from its local struct to get at the parent struct madera.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>