gpio: davinci: Validate the obtained number of IRQs

In the Linux kernel, the following vulnerability has been resolved:

gpio: davinci: Validate the obtained number of IRQs

Value of pdata->gpio_unbanked is taken from Device Tree. In case of broken

DT due to any error this value can be any. Without this value validation

there can be out of chips->irqs array boundaries access in

davinci_gpio_probe().

Validate the obtained nirq value so that it won't exceed the maximum

number of IRQs per bank.

Found by Linux Verification Center (linuxtesting.org) with SVACE.