RDMA/srpt: Do not register event handler until srpt device is fully setup

RDMA/srpt: Do not register event handler until srpt device is fully setup

Upon rare occasions, KASAN reports a use-after-free Write
in srpt_refresh_port().

This seems to be because an event handler is registered before the
srpt device is fully setup and a race condition upon error may leave a
partially setup event handler in place.

Instead, only register the event handler after srpt device initialization
is complete.

Fixes: a42d985bd5b2 ("ib_srpt: Initial SRP Target merge for v3.3-rc1")
Signed-off-by: William Kucharski <william.kucharski@oracle.com>
Link: https://lore.kernel.org/r/20240202091549.991784-2-william.kucharski@oracle.com
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Leon Romanovsky <leon@kernel.org>