staging: comedi: 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 <[e-mail]>
Signed-off-by: Ian Abbott <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/comedi/comedi_buf.c

···
 int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
 			  void *buf, int len, int write)
 {
-	unsigned int pgoff = offset & ~PAGE_MASK;
+	unsigned int pgoff = offset_in_page(offset);
 	unsigned long pg = offset >> PAGE_SHIFT;
 	int done = 0;