xfs: bump INUMBERS cursor correctly in xfs_inumbers_walk

xfs: bump INUMBERS cursor correctly in xfs_inumbers_walk

There's a subtle unit conversion error when we increment the INUMBERS
cursor at the end of xfs_inumbers_walk.  If there's an inode chunk at
the very end of the AG /and/ the AG size is a perfect power of two, the
startino of that last chunk (which is in units of AG inodes) will be 63
less than (1 << agino_log).  If we add XFS_INODES_PER_CHUNK to the
startino, we end up with a startino that's larger than (1 << agino_log)
and when we convert that back to fs inode units we'll rip off that upper
bit and wind up back at the start of the AG.

Fix this by converting to units of fs inodes before adding
XFS_INODES_PER_CHUNK so that we'll harmlessly end up pointing to the
next AG.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>