chunked: fix another occurrence of linkat
chunked: fix another occurrence of linkat

Using unix.AT_EMPTY_PATH requires CAP_DAC_READ_SEARCH.  Use an
equivalent variant that uses /proc/self/fd that can be used with
rootless.

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

containers/storage,containers/storage,containers/storage