tg3: Expand led off fix to include 5720

Commit 989038e2

 ("tg3: Don't turn off
led on 5719 serdes port 0") added code to skip turning led off on port
0 of the 5719 since it powered down other ports. This workaround needs
to be enabled on the 5720 as well.

Cc: stable@vger.kernel.org
Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>