dmaengine: idxd: Fix potential null dereference on pointer status

In the Linux kernel, the following vulnerability has been resolved: dmaengine: idxd: Fix potential null dereference on pointer status There are calls to idxd_cmd_exec that pass a null status pointer however a recent commit has added an assignment to *status that can end up with a null pointer dereference. The function expects a null status pointer sometimes as there is a later assignment to *status where status is first null checked. Fix the issue by null checking status before making the assignment. Addresses-Coverity: ("Explicit null dereferenced")