gpio: aggregator: rename 'name' to 'key' in gpio_aggregator_parse()

gpio: aggregator: rename 'name' to 'key' in gpio_aggregator_parse()

Rename the local variable 'name' in gpio_aggregator_parse() to 'key'
because struct gpio_aggregator_line now uses the 'name' field for the
custom line name and the local variable actually represents a 'key'.
This change prepares for the next but one commit.

No functional change.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Link: https://lore.kernel.org/r/20250407043019.4105613-6-koichiro.den@canonical.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>