hv_netvsc: Fix error handling in netvsc_attach()

If rndis_filter_open() fails, we need to remove the rndis device created
in earlier steps, before returning an error code. Otherwise, the retry of
netvsc_attach() from its callers will fail and hang.

Fixes: 7b2ee50c ("hv_netvsc: common detach logic")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>