staging: lustre: lustre: ptlrpc: Donot initialise null

This patch fixes the following error using checkpatch.pl
Error: Do not initialise statics to 0 or NULL

Signed-off-by: Hema Prathaban <hemaklnce@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>