staging: lustre: Modify arguments of sizeof() to pointer variables

Take the size of a dereference to a variable rather than the associated
type, to make the code more resistant to type changes in the future.
The type of the pointer variable here is the same as the type in the
argument that is being replaced in sizeof().

Signed-off-by: Janani Ravichandran <janani.rvchndrn@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>