media: msi2500: Return queued buffers on start_streaming() failure

Summary

In the Linux kernel, the following vulnerability has been resolved: media: msi2500: 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. msi2500_start_streaming() had five error paths that all hit this trap and were further tangled by ret-overwriting between calls: - -ENODEV when the USB device was already disconnected - -ERESTARTSYS when mutex_lock_interruptible() was interrupted - msi2500_set_usb_adc() failure: ret was silently overwritten by the next call (msi2500_isoc_init), so the error was lost entirely - msi2500_isoc_init() failure: cleanup_queued_bufs was called, but the function then fell through to msi2500_ctrl_msg() and again masked the original error by overwriting ret - msi2500_ctrl_msg(CMD_START_STREAMING) failure: no cleanup at all, leaving isoc URBs submitted with no way for the driver to consume them Consolidate the error paths into a small goto chain. Every failure now stops the function, drains the queued-buffer list, and returns the real error code. The ctrl_msg failure path also rolls back the preceding msi2500_isoc_init() via msi2500_isoc_cleanup() before unlocking and draining. 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").