bug in AT91 MCI suspend routines

This patch fixes a bug in AT91 mmc host driver, that enables the wakeup
from suspend on card detection pin even if the card detect pin is not
available (==0). If not card detection pin is defined, IRQ0 == FIQ gets
enabled and if some activity is present on that pin, the system gets a
FIQ request, that causes a crash.

Signed-off-by: Anti Sullin <anti.sullin@artecdesign.ee>
Signed-off-by: Nicolas Ferre <nicolas.ferre@rfo.atmel.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>