gpio: shared: fix use-after-free bug when adding shared proxies

The GPIO lookup table can stay alive for longer than the kobject whose
name string's address we're assigning to lookup->dev_id. Fix a potential
UAF by duplicating the string.

Cc: stable@vger.kernel.org
Fixes: a060b8c511ab ("gpiolib: implement low-level, shared GPIO support")
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20261014-gpio-shared-fwnode-lookup-v4-1-2253ad645fd6@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>