IB/hfi1: Fix error return code in hfi1_init_dd()

Fix to return a negative error code from the error handling case instead
of 0, as done elsewhere in this function.

Fixes: 4730f4a6

 ("IB/hfi1: Activate the dummy netdev")
Link: https://lore.kernel.org/r/1605249747-17942-1-git-send-email-zhangchangzhong@huawei.com
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>