CVE-2023-52492 dmaengine: fix NULL pointer in channel unregistration function

In the Linux kernel, the following vulnerability has been resolved: dmaengine: fix NULL pointer in channel unregistration function dmaasyncdevicechannelregister can fail. In case of failure, chan-local is freed with freepercpu, and chan-local is nullified. When dmaasyncdeviceunregister is called...