xfs_scrub: refactor inode prefix rendering code

xfs_scrub: refactor inode prefix rendering code

Refactor all the places in the code where we try to render an inode
number as a prefix for some sort of status message.  This will help make
message prefixes more consistent, which should help users to locate
broken metadata.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
[sandeen: rename functions, auto-add spaces, edit comments]
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>