Commit f6eb9b1f, "tg3: Add 5717 asic
rev" changed how the rx return ring size operations are done.  It
effectively inverts the sense of the previous test, but it failed to
also invert the resulting sizes.  This patch corrects that error.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>