net: phy: mdio-sun4i: don't select REGULATOR

The mdio-sun4i driver automatically selects REGULATOR and
REGULATOR_FIXED_VOLTAGE because it uses the regulator API. But a
driver selecting a subsystem increases the chance of generating
circular Kconfig dependencies, especially when other drivers depend on
the selected symbol.

Since the regulator API functions are replaced with no-ops when
REGULATOR is disabled, the driver can be built successfully even
without regulator support and so those 'select' dependencies can be
safely dropped.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Beniamino Galvani <b.galvani@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>