CVE-2026-93086: firmware: arm_scmi: Avoid IDR updates while cleaning channels

In the Linux kernel, the following vulnerability has been resolved: firmware: arm_scmi: Avoid IDR updates while cleaning channels scmi_cleanup_channels() walks the TX/RX channel IDRs with idr_for_each() to free transport resources and destroy the dedicated transport devices before calling idr_destroy(). The destroy callback removed each entry from the same IDR being walked. That is not needed for this cleanup path, and it is unsafe because idr_for_each() has not advanced its radix-tree iterator while the callback is running. Removing the current entry from the callback can invalidate the iterator state. The callback also cannot be protected by rcu_read_lock(), because scmi_device_destroy() may sleep. Leave IDR teardown to the following idr_destroy() call and keep the callback limited to device destruction.