IB/hfi1: Fix hfi1_netdev_rx_init() error handling

The hfi1_vnic_up() function doesn't check whether hfi1_netdev_rx_init()
returns errors.  In hfi1_vnic_init() we need to change the code to
preserve the error code instead of returning success.

Fixes: 2280740f ("IB/hfi1: Virtual Network Interface Controller (VNIC) HW support")
Fixes: 4730f4a6 ("IB/hfi1: Activate the dummy netdev")
Link: https://lore.kernel.org/r/20200530140224.GA1330098@mwanda


Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>