gpio-f7188x: fix chip name and pin count on Nuvoton chip

In fact the device with chip id 0xD283 is called NCT6126D, and that is
the chip id the Nuvoton code was written for. Correct that name to avoid
confusion, because a NCT6116D in fact exists as well but has another
chip id, and is currently not supported.

The look at the spec also revealed that GPIO group7 in fact has 8 pins,
so correct the pin count in that group as well.

Fixes: d0918a84 ("gpio-f7188x: Add GPIO support for Nuvoton NCT6116")
Reported-by: Xing Tong Wu <xingtong.wu@siemens.com>
Signed-off-by: Henning Schild <henning.schild@siemens.com>
Acked-by: Simon Guinot <simon.guinot@sequanux.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>