btrfs: tree-checker: Refactor prev_key check for ino into a function

Refactor the check for prev_key->objectid of the following key types
into one function, check_prev_ino():

- EXTENT_DATA
- INODE_REF
- DIR_INDEX
- DIR_ITEM
- XATTR_ITEM

Also add the check of prev_key for INODE_REF.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>