f2fs: fix to account dirty data in __get_secs_required()

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to account dirty data in __get_secs_required()

It will trigger system panic w/ testcase in [1]:

------------[ cut here ]------------
kernel BUG at fs/f2fs/segment.c:2752!
RIP: 0010:new_curseg+0xc81/0x2110
Call Trace:
f2fs_allocate_data_block+0x1c91/0x4540
do_write_page+0x163/0xdf0
f2fs_outplace_write_data+0x1aa/0x340
f2fs_do_write_data_page+0x797/0x2280
f2fs_write_single_data_page+0x16cd/0x2190
f2fs_write_cache_pages+0x994/0x1c80
f2fs_write_data_pages+0x9cc/0xea0
do_writepages+0x194/0x7a0
filemap_fdatawrite_wbc+0x12b/0x1a0
__filemap_fdatawrite_range+0xbb/0xf0
file_write_and_wait_range+0xa1/0x110
f2fs_do_sync_file+0x26f/0x1c50
f2fs_sync_file+0x12b/0x1d0
vfs_fsync_range+0xfa/0x230
do_fsync+0x3d/0x80
__x64_sys_fsync+0x37/0x50
x64_sys_call+0x1e88/0x20d0
do_syscall_64+0x4b/0x110
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The root cause is if checkpoint_disabling and lfs_mode are both on,
it will trigger OPU for all overwritten data, it may cost more free
segment than expected, so f2fs must account those data correctly to
calculate cosumed free segments later, and return ENOSPC earlier to
avoid run out of free segment during block allocation.

[1] https://lore.kernel.org/fstests/20241015025106.3203676-1-chao@kernel.org/