gpio: 104-idio-16: Use lowercase symbol names for const variables

To prevent confusion, and to match the existing coding style used in
other GPIO drivers, symbol names within the 104-idio-16 GPIO driver
should be lowercase.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>