kernel: wifi: rtl8xxxu: add cancel_work_sync() for c2hcmd_work

A vulnerability was found in the Linux kernel's net rtl8xxxucore.c driver, where a race condition can lead to a use-after-free situation in the rtl8xxxustop function. This occurs when the workqueue is still running but the driver has been stopped and can lead to c2hcmdwork attempting to access...