mmc: atmel-mci: save and restore sdioirq when soft reset is performed

Sometimes a software reset is needed. Then some registers are saved and
restored but the interrupt mask register is missing. It causes issues
with sdio devices whose interrupts are masked after reset.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>