gpiolib: Return label, if set, for IRQ only line

If line has been locked as IRQ without requesting,
still check its label and return it, if not NULL.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240530191418.1138003-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>