ARM: OMAP: add SoSSI clock (remove manual checking of SoSSI state from idle)

The SoSSI driver should already take care of this by enabling / disabling
its clock when necessary, so this legacy callout from the PM idle code
is not needed any more.

Signed-off-by: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>