net: mvpp2: fix the RSS table entry offset

The macro used to access or set an RSS table entry was using an offset
of 8, while it should use an offset of 0. This lead to wrongly configure
the RSS table, not accessing the right entries.

Fixes: 1d7d15d7

 ("net: mvpp2: initialize the RSS tables")
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>