sh: fix the HD64461 level-triggered interrupts handling

Rework the hd64461 demuxer code to fix the HD64461 level-triggered
interrupts handling, using handle_level_irq() as needed.

Signed-off-by: Rafael Ignacio Zurita <rizurita@yahoo.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>