mmc: sdhci: Convert to use sdio_irq_claimed()

Instead of keeping track of whether SDIO IRQs have been enabled via an
internal sdhci status flag, avoid the open-coding and convert into using
sdio_irq_claimed().

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>