mmc: omap_hsmmc: use threaded irq handler for card-detect.

As the card-detect irq handler just schedules work to be done by a
thread, we can use request_threaded_irq to do much of the work for
us.  This means that interrupts which arrive by handle_nested_irq
actually work.

Reviewed-by: Felipe Balbi <balbi@ti.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Kishore Kadiyala <kishorek.kadiyala@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>