cxgb4: fix coccinelle warnings

Commit 16e47624 ("cxgb4: Add new scheme to update T4/T5 firmware")
introduced below coccinelle warning.

>> drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:994:2-8: Replace memcpy with
   struct assignment
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/t4_hw.c

@@ -1120,7 +1120,7 @@ int t4_prep_fw(struct adapter *adap, struct fw_info *fw_info,
 		}
 
 		/* Installed successfully, update the cached header too. */
-		memcpy(card_fw, fs_fw, sizeof(*card_fw));
+		*card_fw = *fs_fw;
 		card_fw_usable = 1;
 		*reset = 0;	/* already reset as part of load_fw */
 	}