accel/amdxdna: Fix crash when destroying a suspended hardware context

In the Linux kernel, the following vulnerability has been resolved: accel/amdxdna: Fix crash when destroying a suspended hardware context If userspace issues an ioctl to destroy a hardware context that has already been automatically suspended, the driver may crash because the mailbox channel pointer is NULL for the suspended context. Fix this by checking the mailbox channel pointer in aie2_destroy_context() before accessing it.