RDMA/cxgb3: Don't allocate the SW queue for user mode CQs

Only kernel mode CQs need the SW queue memory allocated.  The SW queue
for user mode CQs is allocated in userspace by libcxgb3.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>