xfs_repair: junk duplicate hashtab entries when processing sf dirents

xfs_repair: junk duplicate hashtab entries when processing sf dirents

dir_hash_add() adds the passed-in dirent to the directory hashtab even
if there's already a duplicate.  Therefore, if we detect a duplicate or
a garbage entry while processing the a shortform directory's entries, we
need to junk the newly added entry, just like we do when processing
directory data blocks.

This will become particularly relevant in the next patch, where we
generate a master index of parent pointers from the non-junked hashtab
entries of each directory that phase6 scans.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>