fix a warning

| mckernel/kernel/syscall.c: In function 'do_syscall':
| mckernel/kernel/syscall.c:187:
|     warning: 'irqstate' may be used uninitialized in this function

kernel/syscall.c

@@ -194,6 +194,7 @@ long do_syscall(struct syscall_request *req, ihk_mc_user_context_t *ctx,
 	if(proc->nohost) // host is down
 		return -EPIPE;
 
+	irqstate = 0;	/* for avoidance of warning */
 	if(req->number == __NR_exit_group ||
 	   req->number == __NR_gettid ||
 	   req->number == __NR_kill){ // interrupt syscall