fanotify: cleanups around return codes

I just really happen to like

ret = -ENOMEM;
obj = kmalloc()
if (!obj)
	goto out;

As opposed to setting ret inside the conditional.  I also noticed that a
two functions were always returning 0 when they should have been passing
the errors back up the stack.  Fix both.

Signed-off-by: Eric Paris <eparis@redhat.com>