sh: Fix up IRQ re-enabling for the need_resched() case.

In the case where need_resched() is set in between the cpu_idle() and
pm_idle() calls we were missing an else case for just re-enabling local
IRQs and bailing out. This was noticed by the irqs_disabled() warning,
even though IRQs were being re-enabled elsewhere.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>