btrfs: remove unnecessary inode key in btrfs_log_all_parents()

btrfs: remove unnecessary inode key in btrfs_log_all_parents()

We are setting up an inode key to lookup parent directory inode but all we
need is the inode's objectid. The use of the key was necessary in the past
but since commit 0202e83fdab0 ("btrfs: simplify iget helpers") we only
need the objectid.

So remove the key variable in the stack and use instead a simple u64 for
the inode's objectid.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>