xfs_db: pass the inode cluster offset when copying inodes

xfs_db: pass the inode cluster offset when copying inodes

In copy_inode_chunk, we try to determine whether or not an inode is
free as part of copying the inode records.  The macros involved in
testing ir_free require both the inode record and the offset of an
inode within that chunk.  Prior to sparse inode support, the loop
index "i" was also the inode chunk offset; however, when sparse
support was added, "i" became the inode offset within a cluster and
"ioff" became the inode cluster offset within an inode chunk.
Therefore, it is necessary to pass "ioff + i" to do the free-ness
calculation correctly.

This was discovered while trying to take metadumps of fs images for
scrub testing.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>