m32r: Exit ei_handler directly for no IRQ case or IPI operations

If no IRQ request is found in the IRQ check of ei_handler,
we can exit directly by jumping "restore_all", instead of via
"ret_from_intr".

This modification is also likely effective for IPI operations,
because scheduler call never happen at the exit of IPIs.

Signed-off-by: Hitoshi Yamamoto <hitoshiy@linux-m32r.org>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>