xfs_repair: don't dirty inodes unconditionally when testing unlinked state

xfs_repair: don't dirty inodes unconditionally when testing unlinked state

I noticed phase 4 writing back lots of inode buffers during recent
testing. The recent rework of clear_inode() in commit 0724d0f4cb53
("xfs_repair: clear_dinode should simply clear, not check contents")
accidentally caught a call to clear_inode_unlinked() as well,
resulting in all inodes being marked dirty whether then needed
updating or not.

Fix it by making clear_inode_unlinked unconditionally do the clear
(as was done for clear_inode), and move the test to the caller.
Add warnings as well so that this corruption is no longer silently
fixed.

Fixes: 0724d0f ("xfs_repair: clear_dinode should simply clear, ...")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
[sandeen: rework so clear_inode_unlinked is unconditional]
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>