media: uvcvideo: Fix deadlock if uvc_status_stop is called from async_ctrl.work

In the Linux kernel, the following vulnerability has been resolved: media: uvcvideo: Fix deadlock if uvc_status_stop is called from async_ctrl.work If a UVC camera has an asynchronous control, uvc_status_stop may be called from async_ctrl.work: uvc_ctrl_status_event_work() uvc_ctrl_status_event() uvc_ctrl_clear_handle() uvc_pm_put() uvc_status_put() uvc_status_stop() cancel_work_sync() This will cause a deadlock, since cancel_work_sync will wait for uvc_ctrl_status_event_work to complete before returning. Fix this by returning early from uvc_status_stop if we are currently in the work function. flush_status now remains false until uvc_status_start is called again, ensuring that uvc_ctrl_status_event_work won't resubmit the URB.