f2fs: fix to do sanity check on nat entry of quota inode

f2fs: fix to do sanity check on nat entry of quota inode

As Zhiguo reported, nat entry of quota inode could be corrupted:

"ino/block_addr=NULL_ADDR in nid=4 entry"

We'd better to do sanity check on quota inode to detect and record
nat.blk_addr inconsistency, so that we can have a chance to repair
it w/ later fsck.

Reported-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>