sh: fix INTC to use set_irq_chained_handler() for redirects

This patch updates the shared INTC code to use
set_irq_chained_handler() for intc_redirect_irq().

With this in place request_irq() on a merged irq
which has been redirected will now return -EINVAL
instead of 0 together with a crash. This thanks to
the protection of the IRQ_NOREQUEST flag set for
chained interrupt handlers.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>