uml: simplify helper stack handling

run_helper and run_helper_thread had arguments which were the same in all
callers.  run_helper's stack_out was always NULL and run_helper_thread's
stack_order was always 0.  These are now gone, and the constants folded
into the code.

Also fixed leaks of the helper stack in the AIO and SIGIO code.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/drivers/xterm.c b/arch/um/drivers/xterm.c
index 3591284..fd817e5 100644
--- a/arch/um/drivers/xterm.c
+++ b/arch/um/drivers/xterm.c
@@ -132,7 +132,7 @@
 	}
 
 	sprintf(title, data->title, data->device);
-	pid = run_helper(NULL, NULL, argv, NULL);
+	pid = run_helper(NULL, NULL, argv);
 	if (pid < 0) {
 		err = pid;
 		printk(UM_KERN_ERR "xterm_open : run_helper failed, "