btrfs: send: remove unnecessary inode lookup at send_encoded_inline_extent()

We are doing a lookup of the inode but we don't use it at all. So just
remove this pointless lookup.

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