ARM: OMAP4+: Fix bad fallthrough for cpuidle

We don't want to fall through to a bunch of errors for retention
if PM_OMAP4_CPU_OSWR_DISABLE is not configured for a SoC.

Fixes: 6099dd37 ("ARM: OMAP5 / DRA7: Enable CPU RET on suspend")
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>