ubifs: Don't leak orphans on memory during commit

If an orphan has child orphans (xattrs), and due
to a commit the parent orpahn cannot get free()'ed immediately,
put also all child orphans on the erase list.
Otherwise UBIFS will free() them only upon unmount and we
waste memory.

Fixes: 988bec41 ("ubifs: orphan: Handle xattrs like files")
Signed-off-by: Richard Weinberger <richard@nod.at>