qcacmn: Remove assert on serialization timer handler's cmd check

There is an assert inside the serialization timer cb.
This timer cb can also be called in the scheduler context.

So if we get a scan cancel request, it is posted to scheduler
and after that command timesout, the timer  cb is posted
to the scheduler.

So first the cancel is executed and the command is removed.
After that, the timer handler is executed which will find timer->cmd
to NULL.

So, by the time, the timer handler is involved in scheduler context
the command might be cancelled so we return an error when cmd is null
in timer handler cb.

Change-Id: I03651a63de88fe5c6467c5783254ffd006c663d2
CRs-Fixed: 2427323

umac/cmn_services/serialization/src/wlan_serialization_internal.c

@@ -550,8 +550,7 @@ void wlan_serialization_generic_timer_cb(void *arg)
 	struct wlan_serialization_command *cmd = timer->cmd;
 
 	if (!cmd) {
-		ser_err("command not found");
-		QDF_ASSERT(0);
+		ser_err("Command not found");
 		return;
 	}