hns3: fix unused function warning

Without CONFIG_PCI_IOV, we get a harmless warning about an
unused function:

drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_main.c:2273:13: error: 'hclge_disable_sriov' defined but not used [-Werror=unused-function]

The #ifdefs in this driver are obviously wrong, so this just
removes them and uses an IS_ENABLED() check that does the same
thing correctly in a more readable way.

Fixes: 46a3df9f ("net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>