ehea creates memory hotplug, reboot and crash hooks even if there
are no adapters in the box. Just create them when we probe our
first adapter.

[cascardo: use ehea_register_memory_hooks return code]
Signed-off-by: NAnton Blanchard <anton@samba.org>
Tested-by: NThadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>