CVE-2023-53755 dmaengine: ptdma: check for null desc before calling pt_cmd_callback

In the Linux kernel, the following vulnerability has been resolved: dmaengine: ptdma: check for null desc before calling ptcmdcallback Resolves a panic that can occur on AMD systems, typically during host shutdown, after the PTDMA driver had been exercised. The issue was the ptissuepending functi...