RDMA/cma: Fix gcc warning

Building cma.o triggers this gcc warning:

    drivers/infiniband/core/cma.c: In function ‘rdma_resolve_addr’:
    drivers/infiniband/core/cma.c:465:23: warning: ‘port’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    drivers/infiniband/core/cma.c:426:5: note: ‘port’ was declared here

This is a false positive, as "port" will always be initialized if we're
at "found". But if we assign to "id_priv->id.port_num" directly, we can
drop "port". That will, obviously, silence gcc.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>