gpiolib: fix kerneldoc

gpiolib: fix kerneldoc

Add missing '@' to the kernel doc for the new of_node_instance_match
field of struct gpio_chip.

Fixes: bd3ce71078bd ("gpiolib: of: Handle threecell GPIO chips")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/all/20250305203929.70283b9b@canb.auug.org.au/
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250305094939.40011-1-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>