Btrfs: Always use 64bit inode number

There's a potential problem in 32bit system when we exhaust 32bit inode
numbers and start to allocate big inode numbers, because btrfs uses
inode->i_ino in many places.

So here we always use BTRFS_I(inode)->location.objectid, which is an
u64 variable.

There are 2 exceptions that BTRFS_I(inode)->location.objectid !=
inode->i_ino: the btree inode (0 vs 1) and empty subvol dirs (256 vs 2),
and inode->i_ino will be used in those cases.

Another reason to make this change is I'm going to use a special inode
to save free ino cache, and the inode number must be > (u64)-256.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

fs/btrfs/file-item.c

@@ -208,8 +208,9 @@ static int __btrfs_lookup_bio_sums(struct btrfs_root *root,
 						EXTENT_NODATASUM, GFP_NOFS);
 				} else {
 					printk(KERN_INFO "btrfs no csum found "
-					       "for inode %lu start %llu\n",
-					       inode->i_ino,
+					       "for inode %llu start %llu\n",
+					       (unsigned long long)
+					       btrfs_ino(inode),
 					       (unsigned long long)offset);
 				}
 				item = NULL;