staging/octeon: Fix build error without CONFIG_NETDEVICES

While do COMPILE_TEST build without CONFIG_NETDEVICES,
we get Kconfig warning:

WARNING: unmet direct dependencies detected for PHYLIB
  Depends on [n]: NETDEVICES [=n]
  Selected by [y]:
  - OCTEON_ETHERNET [=y] && STAGING [=y] && (CAVIUM_OCTEON_SOC && NETDEVICES [=n] || COMPILE_TEST [=y])
Reported-by: NHulk Robot <hulkci@huawei.com>
Reported-by: NMark Brown <broonie@kernel.org>
Fixes: 171a9bae ("staging/octeon: Allow test build on !MIPS")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/staging/octeon/Kconfig

 # SPDX-License-Identifier: GPL-2.0
 config OCTEON_ETHERNET
 	tristate "Cavium Networks Octeon Ethernet support"
-	depends on CAVIUM_OCTEON_SOC && NETDEVICES || COMPILE_TEST
+	depends on CAVIUM_OCTEON_SOC || COMPILE_TEST
+	depends on NETDEVICES
 	select PHYLIB
 	select MDIO_OCTEON
 	help