gpiolib: cdev: fix uninitialised kfifo

In the Linux kernel, the following vulnerability has been resolved: gpiolib: cdev: fix uninitialised kfifo If a line is requested with debounce, and that results in debouncing in software, and the line is subsequently reconfigured to enable edge detection then the allocation of the kfifo to contain edge events is overlooked. This results in events being written to and read from an uninitialised kfifo. Read events are returned to userspace. Initialise the kfifo in the case where the software debounce is already active.