HID: lg-g15: cancel pending work on remove to fix a use-after-free

In the Linux kernel, the following vulnerability has been resolved: HID: lg-g15: cancel pending work on remove to fix a use-after-free lg_g15_data is allocated with devm and holds a work item. The report handlers schedule that work straight from device input. lg_g15_event() and lg_g15_v2_event() do it on the backlight cycle key, and lg_g510_leds_event() does it too. The worker dereferences the lg_g15_data back through container_of. The driver had no remove callback and never cancelled the work. So if a report scheduled the work and the keyboard was then unplugged, devres freed lg_g15_data while the work was still pending or running, and the worker touched freed memory. This is a use-after-free. It is reachable as a race on device unplug. Add a remove callback that cancels the work before devres frees the state. g15->work is only initialized for the models that schedule it (G15, G15 v2, G510). The G13 and Z-10 leave it zeroed, so guard the cancel on g15->work.func to avoid cancelling a work that was never set up. The g15 NULL test mirrors the one already in lg_g15_raw_event().