ARM: OMAP4: cpuidle - use the omap4_idle_data variable directly

We are storing the 'omap4_idle_data' in the private data field
of the cpuidle device. As we are using this variable only in this file,
that does not really make sense. Let's use the global variable directly.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>