gpio: pcie-idio-24: Fix off-by-one error in get_multiple loop

The PCIe-IDIO-24 features 8 bits of TTL GPIO which may be configured for
output or input. This patch fixes an off-by-one error in the loop
conditional for the get_multiple callback so that the TTL GPIO are
handled.

Fixes: ca370815 ("gpio: pcie-idio-24: Implement get_multiple/set_multiple callbacks")
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>