drivers: interrupt_controller: intc_ioapic: use DEVICE_DT_GET_OR_NULL

The device instance can be obtained at compile time. Here
DEVICE_DT_GET_OR_NULL is used as the following code seems to accept a
NULL condition, meaning instance is optional.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
1 file changed