staging: lustre: fixed ../include/lustre_debug.h is included more than once.

$ make includecheck
./drivers/staging/lustre/lustre/ptlrpc/layout.c: ../include/lustre_debug.h is included more than once.

Signed-off-by: Darryl T. Agostinelli <dagostinelli@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>