CVE-2026-68216: media: pwc: Return queued buffers on start_streaming() failure

In the Linux kernel, the following vulnerability has been resolved: media: pwc: Return queued buffers on start_streaming() failure The vb2 framework hands buffers to the driver via buf_queue() before calling start_streaming(). If start_streaming() returns an error without first returning those buffers via vb2_buffer_done(), vb2_start_streaming() fires WARN_ON(owned_by_drv_count) and the queued buffers leak. pwc's start_streaming() had two early returns that hit this trap: -ENODEV when the USB device was already disconnected, and -ERESTARTSYS when mutex_lock_interruptible() was interrupted by a signal. Call the existing pwc_cleanup_queued_bufs() helper with VB2_BUF_STATE_QUEUED before returning (matching the state already used by the pwc_isoc_init() error path in the same function). This mirrors the uvcvideo fix in commit 4cf3b6fd54eb ("media: uvcvideo: Return queued buffers on start_streaming() failure").