mfd: Use the AB8500's IRQ domain to convert hwirq to virq

Before the AB8500 had its own IRQ domain, the IRQ handler would take
the fired local IRQ (hwirq) and add it to the irq_base to convert it
to an IRQ number which Linux would understand (virq). However, the
IRQ base is not always used anymore since we can make use of Linear
domains. It's better to use the AB8500 hwirq -> virq mapping helper
function to convert them instead. That's what we do here.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>