RDMA/cma: Optimize error handling

Reorganize code relating to cma_get_net_info() and rdam_create_id() to
optimize error case handling (no need to alloc memory/etc. as part of
rdma_create_id() if input parameters are wrong).

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>