xfs_scrub: avoid potential UAF after freeing a duplicate name entry

xfs_scrub: avoid potential UAF after freeing a duplicate name entry

Change the function declaration of unicrash_add to set the caller's
@new_entry to NULL if we detect an updated name entry and do not wish to
continue processing.  This avoids a theoretical UAF if the unicrash_add
caller were to accidentally continue using the pointer.

This isn't an /actual/ UAF because the function formerly set @badflags
to zero, but let's be a little defensive.

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