add_peb_to_free
err = add_peb_to_free(ebh, sleb->pebnr, sleb->erase_cnt);
int add_peb_to_free(struct chfs_ebh *ebh, int pebnr, int ec);
err = add_peb_to_free(ebh, peb->pebnr, peb->erase_cnt);
err = add_peb_to_free(ebh, peb->pebnr, peb->erase_cnt);