cxgb4: Fix MC1 memory offset calculation

Commit 6559a7e8 ("cxgb4: Cleanup macros so they follow the same
style and look consistent") introduced a regression where reading MC1
memory in adapters where MC0 isn't present or MC0 size is not equal to MC1
size caused the adapter to crash due to incorrect computation of memoffset.
Fix is to read the size of MC0 instead of MC1 for offset calculation

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