ARM: OMAP2: Remove redundant check on osc refcount

The usage of the external oscillator is handled already by
sleep_block and doesn't require any extra checking.
Incidentally this fixes a bug where N800 wouldn't enter retention
the first time the display would blank.

Signed-off-by: Klaus Pedersen <klaus.k.pedersen@nokia.com>
Signed-off-by: Igor Stoppa <igor.stoppa@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>