ARM: OMAP: add SoSSI clock (call propagate_rate for childrens)

Clocks with the follow parent rate mode were not updating their
children at propagate rate time.

Signed-off-by: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>