f2fs: do sanity check on fio.new_blkaddr in do_write_page()

F2FS-fs (dm-55): access invalid blkaddr:972878540
Call trace:
 dump_backtrace+0xec/0x128
 show_stack+0x18/0x28
 dump_stack_lvl+0x40/0x88
 dump_stack+0x18/0x24
 __f2fs_is_valid_blkaddr+0x360/0x3b4
 f2fs_is_valid_blkaddr+0x10/0x20
 f2fs_get_node_info+0x21c/0x60c
 __write_node_page+0x15c/0x734
 f2fs_sync_node_pages+0x4f8/0x700
 f2fs_write_checkpoint+0x4a8/0x99c
 __checkpoint_and_complete_reqs+0x7c/0x20c
 issue_checkpoint_thread+0x4c/0xd8
 kthread+0x11c/0x1b0
 ret_from_fork+0x10/0x20

If f2fs_allocate_data_block() fails, we may update nat.blkaddr w/
uninitialized fio.new_blkaddr.

- __write_node_folio
 - f2fs_do_write_node_page
  - do_write_page
   - f2fs_allocate_data_block
   : once it fails, it may not allocate new blkaddr
 - set_node_addr
 : update w/ uninitialized fio.new_blkaddr variable

I've checked all error paths in f2fs_allocate_data_block(), it should
be tagged w/ CP_ERROR_FLAG.

In addition, f2fs_allocate_data_block() succeeds, fio.new_blkaddr should
be valid.

Let's add f2fs_bug_on() to check above two conditions to detect any
potential bugs.

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