ARM: dts: Fix frequency scaling on Gumstix Pepper

The device tree for Gumstix Pepper has DCDC2 and
DCDC3 correctly labelled but the upper limit values
are wrong. The confusion is due to the hardware
quirk where the DCDC2 and DCDC3 wires are flipped
in Pepper.

Signed-off-by: Arun Bharadwaj <arun@gumstix.com>
Tested-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>