IB/ipoib: Fix CONFIG_INFINIBAND_IPOIB_CM

If the above is turned off then ipoib_cm_dev_init unconditionally
returns ENOSYS, and the newly added error handling in
0b3957 prevents ipoib from coming up at all:

kernel: mlx4_0: ipoib_transport_dev_init failed
kernel: mlx4_0: failed to initialize port 1 (ret = -12)

Fixes: 0b39578b

 (IB/ipoib: Use dedicated workqueues per interface)
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>