rdma_create_id() returns ERR_PTR() not null.

Found by smatch (http://repo.or.cz/w/smatch.git).  Compile tested.

regards,
dan carpenter
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>