staging: hp100: Fix build error without ETHERNET

It should depends on ETHERNET, otherwise building fails:

drivers/staging/hp/hp100.o: In function `hp100_pci_remove':
hp100.c:(.text+0x165): undefined reference to `unregister_netdev'
hp100.c:(.text+0x214): undefined reference to `free_netdev'

Fixes: 52340b82 ("hp100: Move 100BaseVG AnyLAN driver to staging")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lore.kernel.org/r/20191113021306.35464-1-yuehaibing@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>