[XFS] Fix potential overflow in xfs_iomap_t delta for very large extents

SGI-PV: 945311
SGI-Modid: xfs-linux-melb:xfs-kern:201708a

Signed-off-by: Eric Sandeen <[e-mail]>
Signed-off-by: Nathan Scott <[e-mail]>

fs/xfs/xfs_iomap.h

···
 	xfs_buftarg_t		*iomap_target;
 	xfs_off_t		iomap_offset;	/* offset of mapping, bytes */
 	xfs_off_t		iomap_bsize;	/* size of mapping, bytes */
-	size_t			iomap_delta;	/* offset into mapping, bytes */
+	xfs_off_t		iomap_delta;	/* offset into mapping, bytes */
 	iomap_flags_t		iomap_flags;
 } xfs_iomap_t;