The RTL8231's gpio_chip.ngpio was set to 36, which is the largest valid
GPIO index. Fix the allowed number of GPIOs by setting ngpio to 37, the
actual line count.

Reported-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Tested-by: Stijn Tintel <stijn@linux-ipv6.be>