mmc: sdhci: Avoid needless loop while handling SDIO interrupts in sdhci_irq

Ignore Card Interrupt bit in the interrupt status if we already
know that mmc_signal_sdio_irq() is going to be called at the end of
sdhci_irq(). This avoids a needless loop in sdhci_irq() repeatedly
reading interrupt status and doing nothing.

Signed-off-by: Alexey Neyman <stilor@att.net>
Acked-by: Dong Aisheng <b29396@freescale.com>
Signed-off-by: Chris Ball <cjb@laptop.org>