migration/rdma: Fix uninitialised rdma_return_path

migration/rdma: Fix uninitialised rdma_return_path

Clang correctly errors out moaning that rdma_return_path
is used uninitialised in the earlier error paths.
Make it NULL so that the error path ignores it.

Fixes: 55cc1b5937a8e709e4c102e74b206281073aab82
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reported-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20180830173657.22939-1-dgilbert@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>