xfs: remove iomap_delta

The iomap_delta field in struct xfs_iomap just contains the
difference between the offset passed to xfs_iomap and the
iomap_offset.  Just calculate it in the only caller that cares.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/xfs_iomap.h

@@ -72,7 +72,6 @@ typedef struct xfs_iomap {
 	xfs_daddr_t		iomap_bn;	/* first 512B blk of mapping */
 	xfs_off_t		iomap_offset;	/* offset of mapping, bytes */
 	xfs_off_t		iomap_bsize;	/* size of mapping, bytes */
-	xfs_off_t		iomap_delta;	/* offset into mapping, bytes */
 	iomap_flags_t		iomap_flags;
 } xfs_iomap_t;