ARM: OMAP: board-omap3beagle: set i2c-3 to 100kHz

Changing it do 100kHz is needed to make more devices works properly. Controlling the
TI DLP Pico projector[1] doesn't work properly at 400kHz, 100kHz and lower work fine.
EDID readout is unaffected by this change.

[1] http://focus.ti.com/dlpdmd/docs/dlpdiscovery.tsp?sectionId=60&tabId=2234

Signed-off-by: Koen Kooi <koen@beagleboard.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>