cxgb4: use the correct max size for firmware flash

The wrong max fw size was being used and causing false
"too big" errors running ethtool -f.
Signed-off-by: NSteve Wise <swise@opengridcomputing.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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

@@ -682,7 +682,7 @@ enum {
 	SF_RD_ID        = 0x9f,       /* read ID */
 	SF_ERASE_SECTOR = 0xd8,       /* erase sector */
 
-	FW_MAX_SIZE = 512 * 1024,
+	FW_MAX_SIZE = 16 * SF_SEC_SIZE,
 };
 
 /**