UserModeLinux-HOWTO.txt: fix a typo

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Richard Weinberger <richard@nod.at>

Documentation/virtual/uml/UserModeLinux-HOWTO.txt

@@ -770,7 +770,7 @@
 
 
 
-  will cause serial line 3 to accept input on the host's /dev/tty3 and
+  will cause serial line 3 to accept input on the host's /dev/tty2 and
   display output on an xterm.  That's a silly example - the most common
   use of this syntax is to reattach the main console to stdin and stdout
   as shown above.