RDMA/core: Delete BUG() from unreachable flow

Remove call to BUG() in case wrong node_type was provided.
This flow is unreachable, because node_types are supplied
from specific enum.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>