irqchip/irq-bcm7038-l1: Gate use of CPU logical map to MIPS

The use of the cpu_logical_map[] array is only relevant for MIPS based
platform where this driver is used as a first level interrupt controller
and contains multiple register groups to map with an associated CPU.

On ARM/ARM64 based systems this interrupt controller is present and used
as a second level interrupt controller hanging off the ARM GIC. That
copy of the interrupt controller contains a single group, resulting in
the intc->cpus[] array to be of size 1.

Things happened to work in that case because we install that interrupt
controller as a chained handler which does not allow it to be affine to
any CPU but the boot CPU which happens to be 0, therefore we never
de-reference past intc->cpus[] but with the current code in place, we do
leave a chance of de-referencing the array past its bounds.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211020184859.2705451-5-f.fainelli@gmail.com