staging: lustre: libcfs: linux: remove unneeded null test before free

Kfree can cope with a null argument, so drop null tests.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@@ expression ptr; @@

- if (ptr != NULL) {
  kfree(ptr);
  ptr = NULL;
- }
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>