nilfs2: add zero-fill for new btree node buffers

Adds missing initialization of newly allocated b-tree node buffers.
This avoids garbage data to be mixed in b-tree node blocks.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/btnode.c

@@ -87,6 +87,7 @@ int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
 			brelse(bh);
 			BUG();
 		}
+		memset(bh->b_data, 0, 1 << inode->i_blkbits);
 		bh->b_bdev = NILFS_I_NILFS(inode)->ns_bdev;
 		bh->b_blocknr = blocknr;
 		set_buffer_mapped(bh);