LU-17187 ldiskfs: use ext4_fsblk_t for block pointers

LU-17187 ldiskfs: use ext4_fsblk_t for block pointers

instead of ext4_lblk_t which is 32bit while actual block
pointers can be larger than 2^32.

Fixes: 0f7e6c02a9 ("LU-16843 ldiskfs: merge extent blocks")
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I201cfa5cb04907eef05bc87abc5701e8aed39d62
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52633
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>