Destination buffer already has offset added.  So, don't add offset
again.

Fetch actual size of configured OBQ from hardware, instead of using
hardcoded value.

Fixes: 7c075ce2 ("cxgb4: collect IBQ and OBQ dumps")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>