gpiolib: Discourage to use formatting strings in line names

Currently the documentation for line names allows to use %u inside
the alternative name. This is broken in character device approach
from day 1 and being in use solely in sysfs.

Character device interface has a line number as a part of its address,
so the users better rely on it. Hence remove the misleading documentation.

On top of that, there are no in-kernel users (out of 6, if I'm correct)
for such names and moreover if one exists it won't help in distinguishing
lines with the same naming as '%u' will also be in them and we will get
a warning in gpiochip_set_desc_names() for such cases.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240505141420.627398-1-andy.shevchenko@gmail.com


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