mmc: sdhci: check interrupt flags in ISR again

When using MSI it is possible that a new MSI is sent while an earlier
MSI is currently handled. In this case SDHCI_INT_STATUS only contains
SDHCI_INT_RESPONSE and the ISR would not be called again. But at the end
of the ISR SDHCI_INT_DATA_END is now also pending which would be ignored.

Fix this by rereading the interrupt flags in the ISR until no interrupt
we care is pending.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>