gpio: Explicitly index samsung_gpio_cfgs

Make it easier to follow the by number references into samsung_gpio_cfgs
by putting the indexes into the code initialising the array, improving
readability a bit. Ideally we wouldn't be using magic array indexes at all
but this is easier than coming up with a better way.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>