Input: ff-core - make use of __free() cleanup facility

Annotate allocated memory with __free(kfree) to simplify the code and
make sure memory is released appropriately.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20241107071538.195340-3-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>