ipc_service: ipc_icbmsg: fix unchecked error in icmsg_open()

Coverity (CID 516253) reported that the return value of
initialize_tx_with_sid_disabled() was set but not used, leading to
potential silent failures.

Check if the return value is negative and propagate the error through the
existing cleanup path.

Fixes: CID 516253

Signed-off-by: Gaetan Perrot <gaetan.perrot@spacecubics.com>