cxgb4 : Update T4/T5/T6 register ranges

Update T4/T5/T6 adapter register ranges so that it doesn't read non
existent registers when dumped using ethtool

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>