PM / AVS: rockchip-io: fix the supply naming for the emmc supply on px30

The supply going to the emmc/flash is named vccio6, not vccio0 and while
the code does this correctly already, the comments and error output do not.

So just change these values to the correct ones.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>