cxgb4: Don't use entire L2T table, use only its slice

The driver was retrieving the parameters for the bounds of its
slice of the L2T from the firmware and then throwing those away and
using the entire table. This corrects that problem.

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