rdma/core: Fix sparse errors

rdma/core: Fix sparse errors

Fix errors reported by sparse in the rdma core stack.  Note that these
are real bugs, but don't affect any existing code.  The mlid issue would
only affect kernel users of rdma_join_multicast which have the rdma_cm
attach/detach its QP.  There are no current in tree users that do this.
(rdma_join_multicast may be used called by user space applications,
which does not have this issue.)  And the pkey setting is simply returned
as informational.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>