f2fs: fix fsck inconsistency caused by FGGC of node block

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

f2fs: fix fsck inconsistency caused by FGGC of node block

During FGGC node block migration, fsck may incorrectly treat the
migrated node block as fsync-written data.

The reproduction scenario:
root@vm:/mnt/f2fs# seq 1 2048 | xargs -n 1 ./test_sync // write inline inode and sync
root@vm:/mnt/f2fs# rm -f 1
root@vm:/mnt/f2fs# sync
root@vm:/mnt/f2fs# f2fs_io gc_range // move data block in sync mode and not write CP
SPO, "fsck --dry-run" find inode has already checkpointed but still
with DENT_BIT_SHIFT set

The root cause is that GC does not clear the dentry mark and fsync mark
during node block migration, leading fsck to misinterpret them as
user-issued fsync writes.

In BGGC mode, node block migration is handled by f2fs_sync_node_pages(),
which guarantees the dentry and fsync marks are cleared before writing.

This patch move the set/clear of the fsync|dentry marks into
__write_node_folio to make the logic clearer, and ensures the
fsync|dentry mark is cleared in FGGC.