gpiolib: Remove redundant assignment of return variable

gpiolib: Remove redundant assignment of return variable

In some functions the returned variable is assigned to 0 and then
reassigned to the actual value. Remove redundant assignments.

In one case make it more clear that the assignment is not needed.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250416095645.2027695-9-andriy.shevchenko@linux.intel.com
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>