gpio: sim: fix an invalid __free() usage

gpio_sim_make_line_names() returns NULL or ERR_PTR() so we must not use
__free(kfree) on the returned address. Split this function into two, one
that determines the size of the "gpio-line-names" array to allocate and
one that actually sets the names at correct offsets. The allocation and
assignment of the managed pointer happens in between.

Fixes: 3faf89f2

 ("gpio: sim: simplify code with cleanup helpers")
Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Closes: https://lore.kernel.org/all/07c32bf1-6c1a-49d9-b97d-f0ae4a2b42ab@p183/
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>