gpiolib: improve coding style for local variables

Drop unneeded whitespaces and put the variables of the same type
together for consistency with the rest of the code.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>