arm: omap3: voltage: fix channel configuration

OMAP3 uses the default settings for VDD1 channel, otherwise the settings will
overlap with VDD2 and attempting to modify VDD1 voltage will actually change
VDD2 voltage.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>