gpiolib: don't double-check the gc->get callback's existence

gpiolib: don't double-check the gc->get callback's existence

gpiochip_get() is called only in two places: in gpio_chip_get_value()
and in gpiochip_get_multiple() where the existence of the gc->get()
callback is already checked. It makes sense to unduplicate the check by
moving it one level up the stack.

Fixes: 86ef402d805d ("gpiolib: sanitize the return value of gpio_chip::get()")
Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Closes: https://lore.kernel.org/all/Z7yekJ8uRh8dphKn@black.fi.intel.com/
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250226-retval-fixes-v2-3-c8dc57182441@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>