media: rtl2832_sdr: Return queued buffers on start_streaming() failure

Summary

In the Linux kernel, the following vulnerability has been resolved: media: rtl2832_sdr: 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. rtl2832_sdr_start_streaming() had multiple error paths that hit this trap: two direct early returns (-ENODEV, -ERESTARTSYS), plus six `goto err` paths covering subdev s_power, tuner setup, ADC setup, stream-buffer allocation, urb allocation, and urb submission failures. None of them returned the queued buffers. The original function had no distinct success exit and fell straight through into the err label, which previously only did mutex_unlock and "return ret". Adding queued-buffer cleanup at err must therefore be paired with an explicit success return; otherwise every successful start would also drain the buffer queue and kill streaming. Add that success return, then add rtl2832_sdr_cleanup_queued_bufs() at the err label and before each early return. The cleanup helper takes a vb2_buffer_state argument so that the start_streaming error paths can pass VB2_BUF_STATE_QUEUED (as expected by userspace on start_streaming failure) while stop_streaming keeps its existing VB2_BUF_STATE_ERROR semantics. This mirrors the uvcvideo fix in commit 4cf3b6fd54eb ("media: uvcvideo: Return queued buffers on start_streaming() failure"). The err label still does not roll back power_ctrl(), frontend_ctrl(), the POWER_ON flag, or stream/URB allocations that may have happened before the failing step. Those are pre-existing leaks of a different class and are not addressed here.