mmc: sh-mmcif: use devm_ for irq management

Use devm_request_threaded_irq() for the host interrupt handlers so we
do not have to worry about freeing them on exit or error. Tidies up the
exit path code for the driver.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>