The root cause of the CWE-125 (Out-of-bounds Read) vulnerability in the given code slice is:

The function `iwl_mvm_mld_rm_sta_from_fw` is likely accessing an array or buffer using the `sta_id` parameter without proper bounds checking. This can lead to reading memory outside the intended array or buffer boundaries if `sta_id` contains an invalid or out-of-range value.

To prevent this vulnerability:

1. Implement input validation for the `sta_id` parameter before passing it to `iwl_mvm_mld_rm_sta_from_fw`.
2. Ensure that `iwl_mvm_mld_rm_sta_from_fw` includes proper bounds checking for any array or buffer access using `sta_id`.
3. Consider using safer data structures or functions that inherently prevent out-of-bounds access.

By addressing these issues, the risk of out-of-bounds read can be mitigated, improving the overall security and stability of the code.