f2fs-tools: fix to check total valid block count before block allocation

f2fs-tools: fix to check total valid block count before block allocation

Now, kernel can catch incorrect total valid block count which is exceed
max user block count of image.

Then, generic/051,476 of fstest reports below message:

Apr 15 11:08:03 szvp000201624 kernel: [ 2533.515813] F2FS-fs (zram1): Wrong valid_user_blocks: 469505, user_block_count: 469504
Apr 15 11:08:03 szvp000201624 kernel: [ 2533.519166] F2FS-fs (zram1): Failed to get valid F2FS checkpoint

The reason is that when fsck repairs corrupted quota sysfile, it didn't
check max user block count when allocating new block for quota sysfile,
so ckpt.valid_block_count can exceed max user block count, result in
mount failure later.

Adding upper boundary check of block count in reserve_new_block() to
fix this issue.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>