Fix an hang on a pipe when run_helper() fails when called by change_tramp()
(i.e.  when calling uml_net) - reproduced the bug and verified this fixes it.
Signed-off-by: NPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>