mmc: sdhci: clean up sdio interrupt enable handling

We don't need to change the SDHCI_SDIO_IRQ_ENABLED flag when we're
merely receiving an interrupt - IRQ handling thread in the MMC core
will either re-enable or disable the interrupt via the enable_sdio_irq
callback, which will update this status appropriately.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>