CVE-2026-80657

In the Linux kernel, the following vulnerability has been resolved:

accel/amdxdna: Guard management mailbox channel cleanup against NULL pointer

The management mailbox channel cleanup helpers can be called from
error handling paths when mgmt_chann has already been destroyed.

Add NULL checks to xdna_mailbox_free_channel() and
xdna_mailbox_stop_channel() so the cleanup path safely returns instead
of dereferencing a NULL mailbox channel pointer.