staging: lustre: lnet: remove null check before kfree

Since kfree(NULL) is safe there is no need to place a check before it.
Issue reported by checkpatch.pl

Signed-off-by: Sumit Pundir <pundirsumit11@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>