Update gpio device path to work with the latest raspbian

[markallanson]

No description provided.

[this-self]

Agree with this PR.

Please add it to master branch.

It would be better if we're using this define

line 19: #define GPIO_CLASS_PATH "/sys/class/gpio/"

for this fix

line 30: int size = snprintf(path, PATH_MAX, GPIO_CLASS_PATH "gpio%u/%s", pin, filename);

[lurch]

Duplicate of #6