f2fs: ensure that node info flags are always initialized

f2fs: ensure that node info flags are always initialized

Syzbot has reported the following KMSAN splat:

BUG: KMSAN: uninit-value in f2fs_new_node_page+0x1494/0x1630
 f2fs_new_node_page+0x1494/0x1630
 f2fs_new_inode_page+0xb9/0x100
 f2fs_init_inode_metadata+0x176/0x1e90
 f2fs_add_inline_entry+0x723/0xc90
 f2fs_do_add_link+0x48f/0xa70
 f2fs_symlink+0x6af/0xfc0
 vfs_symlink+0x1f1/0x470
 do_symlinkat+0x471/0xbc0
 __x64_sys_symlink+0xcf/0x140
 x64_sys_call+0x2fcc/0x3d90
 do_syscall_64+0xd9/0x1b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable new_ni created at:
 f2fs_new_node_page+0x9d/0x1630
 f2fs_new_inode_page+0xb9/0x100

So adjust 'f2fs_get_node_info()' to ensure that 'flag'
field of 'struct node_info' is always initialized.

Reported-by: syzbot+5141f6db57a2f7614352@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5141f6db57a2f7614352
Fixes: e05df3b115e7 ("f2fs: add node operations")
Suggested-by: Chao Yu <chao@kernel.org>
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>