gpio: timberdale: fix off-by-one in IRQ type boundary check

gpio: timberdale: fix off-by-one in IRQ type boundary check

timbgpio_irq_type() currently accepts offset == ngpio, violating
gpiolib's [0..ngpio-1] contract. This can lead to undefined behavior
when computing '1 << offset', and it is also inconsistent with users
that iterate with for_each_set_bit(..., ngpio).

Tighten the upper bound to reject offset == ngpio. No functional change
for in-range offsets.

Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Link: https://lore.kernel.org/r/20250825090850.127163-1-junjie.cao@intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>