ice: remove unused buffer copy code in ice_sq_send_cmd_retry()

The 'buf_cpy'-related code in ice_sq_send_cmd_retry() looks broken.
'buf' is nowhere copied into 'buf_cpy'.

The reason this does not cause problems is that all commands for which
'is_cmd_for_retry' is true go with a NULL buf.

Let's remove 'buf_cpy'. Add a WARN_ON in case the assumption no longer
holds in the future.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>