Btrfs-progs: fsck: force to udate tree root for some cases

Btrfs-progs: fsck: force to udate tree root for some cases

commit roots won't update root item in tree root if it finds
updated root's bytenr is same as before.

However, this is not right for fsck, we need update tree root in
the following case:

1.overwrite previous root node.

2.reinit reloc data tree, this is because we skip pin relo data
 tree before which means we can allocate same block as before.

Fix this by updating tree root ourselves for the above cases.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>