regulator: anatop: Set default voltage selector for vddpu

The code reads the default voltage selector from its register. If the
bootloader disables the regulator, the default voltage selector will be
0 which results in faulty behaviour of this regulator driver.

This patch sets a default voltage selector for vddpu if it is not set in
the register.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org