staging: rdma: hfi1: Use offset_in_page macro

Use offset_in_page macro instead of (var & ~PAGE_MASK)

The Coccinelle semantic patch used to make this change is as follows:
// <smpl>
@@
unsigned long p;
@@
- p & ~PAGE_MASK
+ offset_in_page(p)
// </smpl>

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>