RDMA/ocrdma: Set event's device member in ocrdma_dispatch_ibevent()

We need to set ib_evt.device, or else ib_dispatch_event() will crash
when we call it for unaffiliated events (and consumers may get
confused in their QP/CQ/SRQ event handler for affiliated events).

Also fix sparse warning:

    drivers/infiniband/hw/ocrdma/ocrdma_hw.c:678:36: warning: Using plain integer as NULL pointer

There's no need to clear ib_evt, since every member is initialized.

Signed-off-by: Roland Dreier <roland@purestorage.com>