fwk_put_event chain broken problem

When a cmd sent to SCP from mailbox, usually a serial fwk_put_event will be evoked, if everything goes well, the task will be completed and the last event process function will set the mailbox free to finish the cmd. But if something wrong happen, the fwk_put_event chain will break,and just return err, then no one will set the mailbox free.

as an example, function pd_set_state() in mod_power_domain.c, when user input a invalid state para,it will return FWK_E_PARAM but will not respond to AP, so mailbox will nerver be freed and goes into a deadlock state.

cases above are common in the whole scp project, i think it should respond a error code to AP other than just return, but scp doesn't. it want to know the underlying thought of this processing method, and who should free the mailbox