tg3: Add missed 5719 workaround change

Commit 2866d956, entitled
"tg3: Expand 5719 workaround" extended a 5719 A0 workaround to all
revisions of the chip.  There was a change that should have been a
part of that patch that was missed.  This patch adds the missing
piece.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>