Staging: lustre: Remove int typecast of offsetof().

Remove int typecast of offsetof().
As per below coccinelle rule:

@@
type T;
expression E;
@@
- (int)(offsetof(T,E))
+ offsetof(T,E)

Signed-off-by: Sandhya Bankar <bankarsandhya512@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>