tg3: Off-by-one error in RSS setup

The driver was incorrectly programming the indirection table such that
rx traffic intended for the second ring went to the first ring, rx
traffic intended for the third ring went to the second ring, etc.  This
patch changes the code so that rx traffic is diverted to the proper
ring.

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