sfc: really check hash is valid before using it

Actually hook up the .rx_buf_hash_valid method in EF100's nic_type.

Fixes: 06888543

 ("sfc: check hash is valid before using it")
Reported-by: Martin Habets <mhabets@solarflare.com>
Signed-off-by: Edward Cree <ecree@solarflare.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>