staging/lustre: fix misuse of current->parent.

current->parent is used by ptrace to redirect some signal delivery
to the ptracer.  It should only be used by 'ptrace' or 'signal' code.
All other users should  use current->real_parent, which is the real
parent.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>