net: phy: mdio-bcm-unimac: mark PM functions as __maybe_unused

[ Upstream commit 9b97123a584f60a5bca5a2663485768a1f6cd0a4 ]

The newly added runtime-pm support causes a harmless warning
when CONFIG_PM is disabled:

drivers/net/phy/mdio-bcm-unimac.c:330:12: error: 'unimac_mdio_resume' defined but not used [-Werror=unused-function]
 static int unimac_mdio_resume(struct device *d)
drivers/net/phy/mdio-bcm-unimac.c:321:12: error: 'unimac_mdio_suspend' defined but not used [-Werror=unused-function]
 static int unimac_mdio_suspend(struct device *d)

Marking the functions as __maybe_unused is the easiest workaround
and avoids adding #ifdef checks.

Fixes: b78ac6ecd1b6 ("net: phy: mdio-bcm-unimac: Allow configuring MDIO clock divider")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>