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.

Fixes: 97f2757 ("accel/amdxdna: Fix potential NULL pointer dereference in context cleanup")
Reviewed-by: Karol Wachowski <karol.wachowski@linux.intel.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20260206060306.4050531-1-lizhi.hou@amd.com

Author: houlz0507

drivers/accel/amdxdna/aie2_message.c

@@ -318,6 +318,9 @@ int aie2_destroy_context(struct amdxdna_dev_hdl *ndev, struct amdxdna_hwctx *hwc
 	struct amdxdna_dev *xdna = ndev->xdna;
 	int ret;
 
+	if (!hwctx->priv->mbox_chann)
+		return 0;
+
 	xdna_mailbox_stop_channel(hwctx->priv->mbox_chann);
 	ret = aie2_destroy_context_req(ndev, hwctx->fw_ctx_id);
 	xdna_mailbox_destroy_channel(hwctx->priv->mbox_chann);