gpio: sim: initialize a managed pointer when declaring it

gpio: sim: initialize a managed pointer when declaring it

Variables managed with __free() should typically be initialized where
they are declared so that the __free() callback is paired with its
counterpart resource allocator. Fix the second instance of using
__free() in gpio-sim to follow this pattern.

Fixes: 3faf89f27aab ("gpio: sim: simplify code with cleanup helpers")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>