gpio: free handles in fringe cases

If we fail when copying the ioctl() struct to userspace we still
need to clean up the cruft otherwise left behind or it will stay
around until the issuing process terminates the file handle.

Reported-by: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>