gpiolib: use better errno if get_direction is not available

EINVAL is very generic, use ENOTSUPP in case the gpiochip does not
provide this function. While removing the assignment from the 'status'
variable, use better indentation in the declaration block.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>