fsck.ubifs: Check and correct the index size

fsck.ubifs: Check and correct the index size

This is the 14/18 step of fsck. Check and correct the index size by
traversing TNC just like dbg_check_idx_size does. This step should
be executed after first committing, because 'c->calc_idx_sz' can be
changed in 'ubifs_tnc_start_commit' and the initial value of
'c->calc_idx_sz' read from disk is untrusted.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>